Issue #18702: All skipped tests now reported as skipped.

20 files changed, 1017 insertions, 977 deletions

diff --git a/Lib/test/test_array.py b/Lib/test/test_array.py
index a44ee07ce3..a5c4f23181 100755
--- a/Lib/test/test_array.py
+++ b/Lib/test/test_array.py
@@ -11,6 +11,7 @@ import operator
 import io
 import math
 import struct
+import sys
 import warnings
 
 import array
@@ -993,15 +994,15 @@ class BaseTest:
         s = None
         self.assertRaises(ReferenceError, len, p)
 
+    @unittest.skipUnless(hasattr(sys, 'getrefcount'),
+                         'test needs sys.getrefcount()')
     def test_bug_782369(self):
-        import sys
-        if hasattr(sys, "getrefcount"):
-            for i in range(10):
-                b = array.array('B', range(64))
-            rc = sys.getrefcount(10)
-            for i in range(10):
-                b = array.array('B', range(64))
-            self.assertEqual(rc, sys.getrefcount(10))
+        for i in range(10):
+            b = array.array('B', range(64))
+        rc = sys.getrefcount(10)
+        for i in range(10):
+            b = array.array('B', range(64))
+        self.assertEqual(rc, sys.getrefcount(10))
 
     def test_subclass_with_kwargs(self):
         # SF bug #1486663 -- this used to erroneously raise a TypeError
diff --git a/Lib/test/test_compileall.py b/Lib/test/test_compileall.py
index 2122ade0ae..ff2515df4c 100644
--- a/Lib/test/test_compileall.py
+++ b/Lib/test/test_compileall.py
@@ -40,11 +40,10 @@ class CompileallTests(unittest.TestCase):
         compare = struct.pack('<4sl', importlib.util.MAGIC_NUMBER, mtime)
         return data, compare
 
+    @unittest.skipUnless(hasattr(os, 'stat'), 'test needs os.stat()')
     def recreation_check(self, metadata):
         """Check that compileall recreates bytecode when the new metadata is
         used."""
-        if not hasattr(os, 'stat'):
-            return
         py_compile.compile(self.source_path)
         self.assertEqual(*self.data())
         with open(self.bc_path, 'rb') as file:
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 559e51f47b..cf0b09cbe6 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -905,78 +905,77 @@ Stonecutters Seafood and Chop House+ Lemont+ IL+ 12/19/02+ Week Back
         dialect = sniffer.sniff(self.sample9)
         self.assertTrue(dialect.doublequote)
 
-if not hasattr(sys, "gettotalrefcount"):
-    if support.verbose: print("*** skipping leakage tests ***")
-else:
-    class NUL:
-        def write(s, *args):
-            pass
-        writelines = write
-
-    class TestLeaks(unittest.TestCase):
-        def test_create_read(self):
-            delta = 0
-            lastrc = sys.gettotalrefcount()
-            for i in range(20):
-                gc.collect()
-                self.assertEqual(gc.garbage, [])
-                rc = sys.gettotalrefcount()
-                csv.reader(["a,b,c\r\n"])
-                csv.reader(["a,b,c\r\n"])
-                csv.reader(["a,b,c\r\n"])
-                delta = rc-lastrc
-                lastrc = rc
-            # if csv.reader() leaks, last delta should be 3 or more
-            self.assertEqual(delta < 3, True)
-
-        def test_create_write(self):
-            delta = 0
-            lastrc = sys.gettotalrefcount()
-            s = NUL()
-            for i in range(20):
-                gc.collect()
-                self.assertEqual(gc.garbage, [])
-                rc = sys.gettotalrefcount()
-                csv.writer(s)
-                csv.writer(s)
-                csv.writer(s)
-                delta = rc-lastrc
-                lastrc = rc
-            # if csv.writer() leaks, last delta should be 3 or more
-            self.assertEqual(delta < 3, True)
-
-        def test_read(self):
-            delta = 0
-            rows = ["a,b,c\r\n"]*5
-            lastrc = sys.gettotalrefcount()
-            for i in range(20):
-                gc.collect()
-                self.assertEqual(gc.garbage, [])
-                rc = sys.gettotalrefcount()
-                rdr = csv.reader(rows)
-                for row in rdr:
-                    pass
-                delta = rc-lastrc
-                lastrc = rc
-            # if reader leaks during read, delta should be 5 or more
-            self.assertEqual(delta < 5, True)
-
-        def test_write(self):
-            delta = 0
-            rows = [[1,2,3]]*5
-            s = NUL()
-            lastrc = sys.gettotalrefcount()
-            for i in range(20):
-                gc.collect()
-                self.assertEqual(gc.garbage, [])
-                rc = sys.gettotalrefcount()
-                writer = csv.writer(s)
-                for row in rows:
-                    writer.writerow(row)
-                delta = rc-lastrc
-                lastrc = rc
-            # if writer leaks during write, last delta should be 5 or more
-            self.assertEqual(delta < 5, True)
+class NUL:
+    def write(s, *args):
+        pass
+    writelines = write
+
+@unittest.skipUnless(hasattr(sys, "gettotalrefcount"),
+                     'requires sys.gettotalrefcount()')
+class TestLeaks(unittest.TestCase):
+    def test_create_read(self):
+        delta = 0
+        lastrc = sys.gettotalrefcount()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            csv.reader(["a,b,c\r\n"])
+            csv.reader(["a,b,c\r\n"])
+            csv.reader(["a,b,c\r\n"])
+            delta = rc-lastrc
+            lastrc = rc
+        # if csv.reader() leaks, last delta should be 3 or more
+        self.assertEqual(delta < 3, True)
+
+    def test_create_write(self):
+        delta = 0
+        lastrc = sys.gettotalrefcount()
+        s = NUL()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            csv.writer(s)
+            csv.writer(s)
+            csv.writer(s)
+            delta = rc-lastrc
+            lastrc = rc
+        # if csv.writer() leaks, last delta should be 3 or more
+        self.assertEqual(delta < 3, True)
+
+    def test_read(self):
+        delta = 0
+        rows = ["a,b,c\r\n"]*5
+        lastrc = sys.gettotalrefcount()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            rdr = csv.reader(rows)
+            for row in rdr:
+                pass
+            delta = rc-lastrc
+            lastrc = rc
+        # if reader leaks during read, delta should be 5 or more
+        self.assertEqual(delta < 5, True)
+
+    def test_write(self):
+        delta = 0
+        rows = [[1,2,3]]*5
+        s = NUL()
+        lastrc = sys.gettotalrefcount()
+        for i in range(20):
+            gc.collect()
+            self.assertEqual(gc.garbage, [])
+            rc = sys.gettotalrefcount()
+            writer = csv.writer(s)
+            for row in rows:
+                writer.writerow(row)
+            delta = rc-lastrc
+            lastrc = rc
+        # if writer leaks during write, last delta should be 5 or more
+        self.assertEqual(delta < 5, True)
 
 class TestUnicode(unittest.TestCase):
 
diff --git a/Lib/test/test_dbm_dumb.py b/Lib/test/test_dbm_dumb.py
index e23392959a..208bc4c382 100644
--- a/Lib/test/test_dbm_dumb.py
+++ b/Lib/test/test_dbm_dumb.py
@@ -37,11 +37,9 @@ class DumbDBMTestCase(unittest.TestCase):
         self.read_helper(f)
         f.close()
 
+    @unittest.skipUnless(hasattr(os, 'umask'), 'test needs os.umask()')
+    @unittest.skipUnless(hasattr(os, 'chmod'), 'test needs os.chmod()')
     def test_dumbdbm_creation_mode(self):
-        # On platforms without chmod, don't do anything.
-        if not (hasattr(os, 'chmod') and hasattr(os, 'umask')):
-            return
-
         try:
             old_umask = os.umask(0o002)
             f = dumbdbm.open(_fname, 'c', 0o637)
diff --git a/Lib/test/test_enumerate.py b/Lib/test/test_enumerate.py
index a2d18d01ad..8742afcea8 100644
--- a/Lib/test/test_enumerate.py
+++ b/Lib/test/test_enumerate.py
@@ -202,11 +202,10 @@ class TestReversed(unittest.TestCase, PickleTest):
         self.assertRaises(TypeError, reversed)
         self.assertRaises(TypeError, reversed, [], 'extra')
 
+    @unittest.skipUnless(hasattr(sys, 'getrefcount'), 'test needs sys.getrefcount()')
     def test_bug1229429(self):
         # this bug was never in reversed, it was in
         # PyObject_CallMethod, and reversed_new calls that sometimes.
-        if not hasattr(sys, "getrefcount"):
-            return
         def f():
             pass
         r = f.__reversed__ = object()
diff --git a/Lib/test/test_ftplib.py b/Lib/test/test_ftplib.py
index c0b537a74a..41463e2a5b 100644
--- a/Lib/test/test_ftplib.py
+++ b/Lib/test/test_ftplib.py
@@ -16,7 +16,7 @@ try:
 except ImportError:
     ssl = None
 
-from unittest import TestCase
+from unittest import TestCase, skipUnless
 from test import support
 from test.support import HOST, HOSTv6
 threading = support.import_module('threading')
@@ -780,6 +780,7 @@ class TestFTPClass(TestCase):
         self.assertRaises(ftplib.Error, self.client.storlines, 'stor', f)
 
 
+@skipUnless(support.IPV6_ENABLED, "IPv6 not enabled")
 class TestIPv6Environment(TestCase):
 
     def setUp(self):
@@ -820,6 +821,7 @@ class TestIPv6Environment(TestCase):
         retr()
 
 
+@skipUnless(ssl, "SSL not available")
 class TestTLS_FTPClassMixin(TestFTPClass):
     """Repeat TestFTPClass tests starting the TLS layer for both control
     and data connections first.
@@ -835,6 +837,7 @@ class TestTLS_FTPClassMixin(TestFTPClass):
         self.client.prot_p()
 
 
+@skipUnless(ssl, "SSL not available")
 class TestTLS_FTPClass(TestCase):
     """Specific TLS_FTP class tests."""
 
@@ -1027,12 +1030,9 @@ class TestNetrcDeprecation(TestCase):
 
 
 def test_main():
-    tests = [TestFTPClass, TestTimeouts, TestNetrcDeprecation]
-    if support.IPV6_ENABLED:
-        tests.append(TestIPv6Environment)
-
-    if ssl is not None:
-        tests.extend([TestTLS_FTPClassMixin, TestTLS_FTPClass])
+    tests = [TestFTPClass, TestTimeouts, TestNetrcDeprecation,
+             TestIPv6Environment,
+             TestTLS_FTPClassMixin, TestTLS_FTPClass]
 
     thread_info = support.threading_setup()
     try:
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 6c679ce436..78e2a30dbc 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -868,10 +868,10 @@ class TestMaildir(TestMailbox, unittest.TestCase):
         for msg in self._box:
             pass
 
+    @unittest.skipUnless(hasattr(os, 'umask'), 'test needs os.umask()')
+    @unittest.skipUnless(hasattr(os, 'stat'), 'test needs os.stat()')
     def test_file_permissions(self):
         # Verify that message files are created without execute permissions
-        if not hasattr(os, "stat") or not hasattr(os, "umask"):
-            return
         msg = mailbox.MaildirMessage(self._template % 0)
         orig_umask = os.umask(0)
         try:
@@ -882,12 +882,11 @@ class TestMaildir(TestMailbox, unittest.TestCase):
         mode = os.stat(path).st_mode
         self.assertFalse(mode & 0o111)
 
+    @unittest.skipUnless(hasattr(os, 'umask'), 'test needs os.umask()')
+    @unittest.skipUnless(hasattr(os, 'stat'), 'test needs os.stat()')
     def test_folder_file_perms(self):
         # From bug #3228, we want to verify that the file created inside a Maildir
         # subfolder isn't marked as executable.
-        if not hasattr(os, "stat") or not hasattr(os, "umask"):
-            return
-
         orig_umask = os.umask(0)
         try:
             subfolder = self._box.add_folder('subfolder')
@@ -1097,24 +1096,25 @@ class TestMbox(_TestMboxMMDF, unittest.TestCase):
 
     _factory = lambda self, path, factory=None: mailbox.mbox(path, factory)
 
+    @unittest.skipUnless(hasattr(os, 'umask'), 'test needs os.umask()')
+    @unittest.skipUnless(hasattr(os, 'stat'), 'test needs os.stat()')
     def test_file_perms(self):
         # From bug #3228, we want to verify that the mailbox file isn't executable,
         # even if the umask is set to something that would leave executable bits set.
         # We only run this test on platforms that support umask.
-        if hasattr(os, 'umask') and hasattr(os, 'stat'):
-            try:
-                old_umask = os.umask(0o077)
-                self._box.close()
-                os.unlink(self._path)
-                self._box = mailbox.mbox(self._path, create=True)
-                self._box.add('')
-                self._box.close()
-            finally:
-                os.umask(old_umask)
+        try:
+            old_umask = os.umask(0o077)
+            self._box.close()
+            os.unlink(self._path)
+            self._box = mailbox.mbox(self._path, create=True)
+            self._box.add('')
+            self._box.close()
+        finally:
+            os.umask(old_umask)
 
-            st = os.stat(self._path)
-            perms = st.st_mode
-            self.assertFalse((perms & 0o111)) # Execute bits should all be off.
+        st = os.stat(self._path)
+        perms = st.st_mode
+        self.assertFalse((perms & 0o111)) # Execute bits should all be off.
 
     def test_terminating_newline(self):
         message = email.message.Message()
diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index 715003af05..48f84ba732 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -980,38 +980,37 @@ class MathTests(unittest.TestCase):
     # still fails this part of the test on some platforms.  For now, we only
     # *run* test_exceptions() in verbose mode, so that this isn't normally
     # tested.
+    @unittest.skipUnless(verbose, 'requires verbose mode')
+    def test_exceptions(self):
+        try:
+            x = math.exp(-1000000000)
+        except:
+            # mathmodule.c is failing to weed out underflows from libm, or
+            # we've got an fp format with huge dynamic range
+            self.fail("underflowing exp() should not have raised "
+                        "an exception")
+        if x != 0:
+            self.fail("underflowing exp() should have returned 0")
+
+        # If this fails, probably using a strict IEEE-754 conforming libm, and x
+        # is +Inf afterwards.  But Python wants overflows detected by default.
+        try:
+            x = math.exp(1000000000)
+        except OverflowError:
+            pass
+        else:
+            self.fail("overflowing exp() didn't trigger OverflowError")
 
-    if verbose:
-        def test_exceptions(self):
-            try:
-                x = math.exp(-1000000000)
-            except:
-                # mathmodule.c is failing to weed out underflows from libm, or
-                # we've got an fp format with huge dynamic range
-                self.fail("underflowing exp() should not have raised "
-                          "an exception")
-            if x != 0:
-                self.fail("underflowing exp() should have returned 0")
-
-            # If this fails, probably using a strict IEEE-754 conforming libm, and x
-            # is +Inf afterwards.  But Python wants overflows detected by default.
-            try:
-                x = math.exp(1000000000)
-            except OverflowError:
-                pass
-            else:
-                self.fail("overflowing exp() didn't trigger OverflowError")
-
-            # If this fails, it could be a puzzle.  One odd possibility is that
-            # mathmodule.c's macros are getting confused while comparing
-            # Inf (HUGE_VAL) to a NaN, and artificially setting errno to ERANGE
-            # as a result (and so raising OverflowError instead).
-            try:
-                x = math.sqrt(-1.0)
-            except ValueError:
-                pass
-            else:
-                self.fail("sqrt(-1) didn't raise ValueError")
+        # If this fails, it could be a puzzle.  One odd possibility is that
+        # mathmodule.c's macros are getting confused while comparing
+        # Inf (HUGE_VAL) to a NaN, and artificially setting errno to ERANGE
+        # as a result (and so raising OverflowError instead).
+        try:
+            x = math.sqrt(-1.0)
+        except ValueError:
+            pass
+        else:
+            self.fail("sqrt(-1) didn't raise ValueError")
 
     @requires_IEEE_754
     def test_testfile(self):
diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
index b1cc97371e..6ca5e1b730 100644
--- a/Lib/test/test_mmap.py
+++ b/Lib/test/test_mmap.py
@@ -315,26 +315,25 @@ class MmapTests(unittest.TestCase):
         mf.close()
         f.close()
 
+    @unittest.skipUnless(hasattr(os, "stat"), "needs os.stat()")
     def test_entire_file(self):
         # test mapping of entire file by passing 0 for map length
-        if hasattr(os, "stat"):
-            f = open(TESTFN, "wb+")
+        f = open(TESTFN, "wb+")
 
-            f.write(2**16 * b'm') # Arbitrary character
-            f.close()
+        f.write(2**16 * b'm') # Arbitrary character
+        f.close()
 
-            f = open(TESTFN, "rb+")
-            mf = mmap.mmap(f.fileno(), 0)
-            self.assertEqual(len(mf), 2**16, "Map size should equal file size.")
-            self.assertEqual(mf.read(2**16), 2**16 * b"m")
-            mf.close()
-            f.close()
+        f = open(TESTFN, "rb+")
+        mf = mmap.mmap(f.fileno(), 0)
+        self.assertEqual(len(mf), 2**16, "Map size should equal file size.")
+        self.assertEqual(mf.read(2**16), 2**16 * b"m")
+        mf.close()
+        f.close()
 
+    @unittest.skipUnless(hasattr(os, "stat"), "needs os.stat()")
     def test_length_0_offset(self):
         # Issue #10916: test mapping of remainder of file by passing 0 for
         # map length with an offset doesn't cause a segfault.
-        if not hasattr(os, "stat"):
-            self.skipTest("needs os.stat")
         # NOTE: allocation granularity is currently 65536 under Win64,
         # and therefore the minimum offset alignment.
         with open(TESTFN, "wb") as f:
@@ -344,12 +343,10 @@ class MmapTests(unittest.TestCase):
             with mmap.mmap(f.fileno(), 0, offset=65536, access=mmap.ACCESS_READ) as mf:
                 self.assertRaises(IndexError, mf.__getitem__, 80000)
 
+    @unittest.skipUnless(hasattr(os, "stat"), "needs os.stat()")
     def test_length_0_large_offset(self):
         # Issue #10959: test mapping of a file by passing 0 for
         # map length with a large offset doesn't cause a segfault.
-        if not hasattr(os, "stat"):
-            self.skipTest("needs os.stat")
-
         with open(TESTFN, "wb") as f:
             f.write(115699 * b'm') # Arbitrary character
 
@@ -561,9 +558,8 @@ class MmapTests(unittest.TestCase):
                 return mmap.mmap.__new__(klass, -1, *args, **kwargs)
         anon_mmap(PAGESIZE)
 
+    @unittest.skipUnless(hasattr(mmap, 'PROT_READ'), "needs mmap.PROT_READ")
     def test_prot_readonly(self):
-        if not hasattr(mmap, 'PROT_READ'):
-            return
         mapsize = 10
         with open(TESTFN, "wb") as fp:
             fp.write(b"a"*mapsize)
@@ -617,67 +613,69 @@ class MmapTests(unittest.TestCase):
             self.assertEqual(m.read_byte(), b)
             m.close()
 
-    if os.name == 'nt':
-        def test_tagname(self):
-            data1 = b"0123456789"
-            data2 = b"abcdefghij"
-            assert len(data1) == len(data2)
-
-            # Test same tag
-            m1 = mmap.mmap(-1, len(data1), tagname="foo")
-            m1[:] = data1
-            m2 = mmap.mmap(-1, len(data2), tagname="foo")
-            m2[:] = data2
-            self.assertEqual(m1[:], data2)
-            self.assertEqual(m2[:], data2)
-            m2.close()
-            m1.close()
-
-            # Test different tag
-            m1 = mmap.mmap(-1, len(data1), tagname="foo")
-            m1[:] = data1
-            m2 = mmap.mmap(-1, len(data2), tagname="boo")
-            m2[:] = data2
-            self.assertEqual(m1[:], data1)
-            self.assertEqual(m2[:], data2)
-            m2.close()
-            m1.close()
-
-        def test_crasher_on_windows(self):
-            # Should not crash (Issue 1733986)
-            m = mmap.mmap(-1, 1000, tagname="foo")
-            try:
-                mmap.mmap(-1, 5000, tagname="foo")[:] # same tagname, but larger size
-            except:
-                pass
-            m.close()
+    @unittest.skipUnless(os.name == 'nt', 'requires Windows')
+    def test_tagname(self):
+        data1 = b"0123456789"
+        data2 = b"abcdefghij"
+        assert len(data1) == len(data2)
+
+        # Test same tag
+        m1 = mmap.mmap(-1, len(data1), tagname="foo")
+        m1[:] = data1
+        m2 = mmap.mmap(-1, len(data2), tagname="foo")
+        m2[:] = data2
+        self.assertEqual(m1[:], data2)
+        self.assertEqual(m2[:], data2)
+        m2.close()
+        m1.close()
+
+        # Test different tag
+        m1 = mmap.mmap(-1, len(data1), tagname="foo")
+        m1[:] = data1
+        m2 = mmap.mmap(-1, len(data2), tagname="boo")
+        m2[:] = data2
+        self.assertEqual(m1[:], data1)
+        self.assertEqual(m2[:], data2)
+        m2.close()
+        m1.close()
+
+    @unittest.skipUnless(os.name == 'nt', 'requires Windows')
+    def test_crasher_on_windows(self):
+        # Should not crash (Issue 1733986)
+        m = mmap.mmap(-1, 1000, tagname="foo")
+        try:
+            mmap.mmap(-1, 5000, tagname="foo")[:] # same tagname, but larger size
+        except:
+            pass
+        m.close()
 
-            # Should not crash (Issue 5385)
-            with open(TESTFN, "wb") as fp:
-                fp.write(b"x"*10)
-            f = open(TESTFN, "r+b")
-            m = mmap.mmap(f.fileno(), 0)
-            f.close()
-            try:
-                m.resize(0) # will raise OSError
-            except:
-                pass
-            try:
-                m[:]
-            except:
-                pass
-            m.close()
+        # Should not crash (Issue 5385)
+        with open(TESTFN, "wb") as fp:
+            fp.write(b"x"*10)
+        f = open(TESTFN, "r+b")
+        m = mmap.mmap(f.fileno(), 0)
+        f.close()
+        try:
+            m.resize(0) # will raise OSError
+        except:
+            pass
+        try:
+            m[:]
+        except:
+            pass
+        m.close()
 
-        def test_invalid_descriptor(self):
-            # socket file descriptors are valid, but out of range
-            # for _get_osfhandle, causing a crash when validating the
-            # parameters to _get_osfhandle.
-            s = socket.socket()
-            try:
-                with self.assertRaises(OSError):
-                    m = mmap.mmap(s.fileno(), 10)
-            finally:
-                s.close()
+    @unittest.skipUnless(os.name == 'nt', 'requires Windows')
+    def test_invalid_descriptor(self):
+        # socket file descriptors are valid, but out of range
+        # for _get_osfhandle, causing a crash when validating the
+        # parameters to _get_osfhandle.
+        s = socket.socket()
+        try:
+            with self.assertRaises(OSError):
+                m = mmap.mmap(s.fileno(), 10)
+        finally:
+            s.close()
 
     def test_context_manager(self):
         with mmap.mmap(-1, 10) as m:
diff --git a/Lib/test/test_nntplib.py b/Lib/test/test_nntplib.py
index d00c9db28f..71a4ec022b 100644
--- a/Lib/test/test_nntplib.py
+++ b/Lib/test/test_nntplib.py
@@ -6,10 +6,12 @@ import unittest
 import functools
 import contextlib
 from test import support
-from nntplib import NNTP, GroupInfo, _have_ssl
+from nntplib import NNTP, GroupInfo
 import nntplib
-if _have_ssl:
+try:
     import ssl
+except ImportError:
+    ssl = None
 
 TIMEOUT = 30
 
@@ -199,23 +201,23 @@ class NetworkedNNTPTestsMixin:
         resp, caps = self.server.capabilities()
         _check_caps(caps)
 
-    if _have_ssl:
-        def test_starttls(self):
-            file = self.server.file
-            sock = self.server.sock
-            try:
-                self.server.starttls()
-            except nntplib.NNTPPermanentError:
-                self.skipTest("STARTTLS not supported by server.")
-            else:
-                # Check that the socket and internal pseudo-file really were
-                # changed.
-                self.assertNotEqual(file, self.server.file)
-                self.assertNotEqual(sock, self.server.sock)
-                # Check that the new socket really is an SSL one
-                self.assertIsInstance(self.server.sock, ssl.SSLSocket)
-                # Check that trying starttls when it's already active fails.
-                self.assertRaises(ValueError, self.server.starttls)
+    @unittest.skipUnless(ssl, 'requires SSL support')
+    def test_starttls(self):
+        file = self.server.file
+        sock = self.server.sock
+        try:
+            self.server.starttls()
+        except nntplib.NNTPPermanentError:
+            self.skipTest("STARTTLS not supported by server.")
+        else:
+            # Check that the socket and internal pseudo-file really were
+            # changed.
+            self.assertNotEqual(file, self.server.file)
+            self.assertNotEqual(sock, self.server.sock)
+            # Check that the new socket really is an SSL one
+            self.assertIsInstance(self.server.sock, ssl.SSLSocket)
+            # Check that trying starttls when it's already active fails.
+            self.assertRaises(ValueError, self.server.starttls)
 
     def test_zlogin(self):
         # This test must be the penultimate because further commands will be
@@ -300,25 +302,24 @@ class NetworkedNNTPTests(NetworkedNNTPTestsMixin, unittest.TestCase):
         if cls.server is not None:
             cls.server.quit()
 
+@unittest.skipUnless(ssl, 'requires SSL support')
+class NetworkedNNTP_SSLTests(NetworkedNNTPTests):
 
-if _have_ssl:
-    class NetworkedNNTP_SSLTests(NetworkedNNTPTests):
-
-        # Technical limits for this public NNTP server (see http://www.aioe.org):
-        # "Only two concurrent connections per IP address are allowed and
-        # 400 connections per day are accepted from each IP address."
+    # Technical limits for this public NNTP server (see http://www.aioe.org):
+    # "Only two concurrent connections per IP address are allowed and
+    # 400 connections per day are accepted from each IP address."
 
-        NNTP_HOST = 'nntp.aioe.org'
-        GROUP_NAME = 'comp.lang.python'
-        GROUP_PAT = 'comp.lang.*'
+    NNTP_HOST = 'nntp.aioe.org'
+    GROUP_NAME = 'comp.lang.python'
+    GROUP_PAT = 'comp.lang.*'
 
-        NNTP_CLASS = nntplib.NNTP_SSL
+    NNTP_CLASS = getattr(nntplib, 'NNTP_SSL', None)
 
-        # Disabled as it produces too much data
-        test_list = None
+    # Disabled as it produces too much data
+    test_list = None
 
-        # Disabled as the connection will already be encrypted.
-        test_starttls = None
+    # Disabled as the connection will already be encrypted.
+    test_starttls = None
 
 
 #
@@ -1407,12 +1408,13 @@ class MiscTests(unittest.TestCase):
         gives(2000, 6, 23, "000623", "000000")
         gives(2010, 6, 5, "100605", "000000")
 
+    @unittest.skipUnless(ssl, 'requires SSL support')
+    def test_ssl_support(self):
+        self.assertTrue(hasattr(nntplib, 'NNTP_SSL'))
 
 def test_main():
     tests = [MiscTests, NNTPv1Tests, NNTPv2Tests, CapsAfterLoginNNTPv2Tests,
-            SendReaderNNTPv2Tests, NetworkedNNTPTests]
-    if _have_ssl:
-        tests.append(NetworkedNNTP_SSLTests)
+            SendReaderNNTPv2Tests, NetworkedNNTPTests, NetworkedNNTP_SSLTests]
     support.run_unittest(*tests)
 
 
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 81a4d9a7e2..1ffa7dafeb 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -185,10 +185,8 @@ class StatAttributeTests(unittest.TestCase):
         os.unlink(self.fname)
         os.rmdir(support.TESTFN)
 
+    @unittest.skipUnless(hasattr(os, 'stat'), 'test needs os.stat()')
     def check_stat_attributes(self, fname):
-        if not hasattr(os, "stat"):
-            return
-
         result = os.stat(fname)
 
         # Make sure direct access works
@@ -272,10 +270,8 @@ class StatAttributeTests(unittest.TestCase):
         unpickled = pickle.loads(p)
         self.assertEqual(result, unpickled)
 
+    @unittest.skipUnless(hasattr(os, 'statvfs'), 'test needs os.statvfs()')
     def test_statvfs_attributes(self):
-        if not hasattr(os, "statvfs"):
-            return
-
         try:
             result = os.statvfs(self.fname)
         except OSError as e:
@@ -479,10 +475,10 @@ class StatAttributeTests(unittest.TestCase):
                 os.close(dirfd)
         self._test_utime_subsecond(set_time)
 
-    # Restrict test to Win32, since there is no guarantee other
+    # Restrict tests to Win32, since there is no guarantee other
     # systems support centiseconds
-    if sys.platform == 'win32':
-        def get_file_system(path):
+    def get_file_system(path):
+        if sys.platform == 'win32':
             root = os.path.splitdrive(os.path.abspath(path))[0] + '\\'
             import ctypes
             kernel32 = ctypes.windll.kernel32
@@ -490,38 +486,45 @@ class StatAttributeTests(unittest.TestCase):
             if kernel32.GetVolumeInformationW(root, None, 0, None, None, None, buf, len(buf)):
                 return buf.value
 
-        if get_file_system(support.TESTFN) == "NTFS":
-            def test_1565150(self):
-                t1 = 1159195039.25
-                os.utime(self.fname, (t1, t1))
-                self.assertEqual(os.stat(self.fname).st_mtime, t1)
-
-            def test_large_time(self):
-                t1 = 5000000000 # some day in 2128
-                os.utime(self.fname, (t1, t1))
-                self.assertEqual(os.stat(self.fname).st_mtime, t1)
-
-        def test_1686475(self):
-            # Verify that an open file can be stat'ed
-            try:
-                os.stat(r"c:\pagefile.sys")
-            except FileNotFoundError:
-                pass # file does not exist; cannot run test
-            except OSError as e:
-                self.fail("Could not stat pagefile.sys")
+    @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
+    @unittest.skipUnless(get_file_system(support.TESTFN) == "NTFS",
+                         "requires NTFS")
+    def test_1565150(self):
+        t1 = 1159195039.25
+        os.utime(self.fname, (t1, t1))
+        self.assertEqual(os.stat(self.fname).st_mtime, t1)
+
+    @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
+    @unittest.skipUnless(get_file_system(support.TESTFN) == "NTFS",
+                         "requires NTFS")
+    def test_large_time(self):
+        t1 = 5000000000 # some day in 2128
+        os.utime(self.fname, (t1, t1))
+        self.assertEqual(os.stat(self.fname).st_mtime, t1)
+
+    @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
+    def test_1686475(self):
+        # Verify that an open file can be stat'ed
+        try:
+            os.stat(r"c:\pagefile.sys")
+        except FileNotFoundError:
+            pass # file does not exist; cannot run test
+        except OSError as e:
+            self.fail("Could not stat pagefile.sys")
 
-        @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
-        def test_15261(self):
-            # Verify that stat'ing a closed fd does not cause crash
-            r, w = os.pipe()
-            try:
-                os.stat(r)          # should not raise error
-            finally:
-                os.close(r)
-                os.close(w)
-            with self.assertRaises(OSError) as ctx:
-                os.stat(r)
-            self.assertEqual(ctx.exception.errno, errno.EBADF)
+    @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
+    @unittest.skipUnless(hasattr(os, "pipe"), "requires os.pipe()")
+    def test_15261(self):
+        # Verify that stat'ing a closed fd does not cause crash
+        r, w = os.pipe()
+        try:
+            os.stat(r)          # should not raise error
+        finally:
+            os.close(r)
+            os.close(w)
+        with self.assertRaises(OSError) as ctx:
+            os.stat(r)
+        self.assertEqual(ctx.exception.errno, errno.EBADF)
 
 from test import mapping_tests
 
@@ -1167,6 +1170,7 @@ class ExecTests(unittest.TestCase):
             self._test_internal_execvpe(bytes)
 
 
+@unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
 class Win32ErrorTests(unittest.TestCase):
     def test_rename(self):
         self.assertRaises(OSError, os.rename, support.TESTFN, support.TESTFN+".bak")
@@ -1213,63 +1217,63 @@ class TestInvalidFD(unittest.TestCase):
             self.fail("%r didn't raise a OSError with a bad file descriptor"
                       % f)
 
+    @unittest.skipUnless(hasattr(os, 'isatty'), 'test needs os.isatty()')
     def test_isatty(self):
-        if hasattr(os, "isatty"):
-            self.assertEqual(os.isatty(support.make_bad_fd()), False)
+        self.assertEqual(os.isatty(support.make_bad_fd()), False)
 
+    @unittest.skipUnless(hasattr(os, 'closerange'), 'test needs os.closerange()')
     def test_closerange(self):
-        if hasattr(os, "closerange"):
-            fd = support.make_bad_fd()
-            # Make sure none of the descriptors we are about to close are
-            # currently valid (issue 6542).
-            for i in range(10):
-                try: os.fstat(fd+i)
-                except OSError:
-                    pass
-                else:
-                    break
-            if i < 2:
-                raise unittest.SkipTest(
-                    "Unable to acquire a range of invalid file descriptors")
-            self.assertEqual(os.closerange(fd, fd + i-1), None)
+        fd = support.make_bad_fd()
+        # Make sure none of the descriptors we are about to close are
+        # currently valid (issue 6542).
+        for i in range(10):
+            try: os.fstat(fd+i)
+            except OSError:
+                pass
+            else:
+                break
+        if i < 2:
+            raise unittest.SkipTest(
+                "Unable to acquire a range of invalid file descriptors")
+        self.assertEqual(os.closerange(fd, fd + i-1), None)
 
+    @unittest.skipUnless(hasattr(os, 'dup2'), 'test needs os.dup2()')
     def test_dup2(self):
-        if hasattr(os, "dup2"):
-            self.check(os.dup2, 20)
+        self.check(os.dup2, 20)
 
+    @unittest.skipUnless(hasattr(os, 'fchmod'), 'test needs os.fchmod()')
     def test_fchmod(self):
-        if hasattr(os, "fchmod"):
-            self.check(os.fchmod, 0)
+        self.check(os.fchmod, 0)
 
+    @unittest.skipUnless(hasattr(os, 'fchown'), 'test needs os.fchown()')
     def test_fchown(self):
-        if hasattr(os, "fchown"):
-            self.check(os.fchown, -1, -1)
+        self.check(os.fchown, -1, -1)
 
+    @unittest.skipUnless(hasattr(os, 'fpathconf'), 'test needs os.fpathconf()')
     def test_fpathconf(self):
-        if hasattr(os, "fpathconf"):
-            self.check(os.pathconf, "PC_NAME_MAX")
-            self.check(os.fpathconf, "PC_NAME_MAX")
+        self.check(os.pathconf, "PC_NAME_MAX")
+        self.check(os.fpathconf, "PC_NAME_MAX")
 
+    @unittest.skipUnless(hasattr(os, 'ftruncate'), 'test needs os.ftruncate()')
     def test_ftruncate(self):
-        if hasattr(os, "ftruncate"):
-            self.check(os.truncate, 0)
-            self.check(os.ftruncate, 0)
+        self.check(os.truncate, 0)
+        self.check(os.ftruncate, 0)
 
+    @unittest.skipUnless(hasattr(os, 'lseek'), 'test needs os.lseek()')
     def test_lseek(self):
-        if hasattr(os, "lseek"):
-            self.check(os.lseek, 0, 0)
+        self.check(os.lseek, 0, 0)
 
+    @unittest.skipUnless(hasattr(os, 'read'), 'test needs os.read()')
     def test_read(self):
-        if hasattr(os, "read"):
-            self.check(os.read, 1)
+        self.check(os.read, 1)
 
+    @unittest.skipUnless(hasattr(os, 'tcsetpgrp'), 'test needs os.tcsetpgrp()')
     def test_tcsetpgrpt(self):
-        if hasattr(os, "tcsetpgrp"):
-            self.check(os.tcsetpgrp, 0)
+        self.check(os.tcsetpgrp, 0)
 
+    @unittest.skipUnless(hasattr(os, 'write'), 'test needs os.write()')
     def test_write(self):
-        if hasattr(os, "write"):
-            self.check(os.write, b" ")
+        self.check(os.write, b" ")
 
 
 class LinkTests(unittest.TestCase):
@@ -1309,138 +1313,133 @@ class LinkTests(unittest.TestCase):
         self.file2 = self.file1 + "2"
         self._test_link(self.file1, self.file2)
 
-if sys.platform != 'win32':
-    class Win32ErrorTests(unittest.TestCase):
-        pass
-
-    class PosixUidGidTests(unittest.TestCase):
-        if hasattr(os, 'setuid'):
-            def test_setuid(self):
-                if os.getuid() != 0:
-                    self.assertRaises(OSError, os.setuid, 0)
-                self.assertRaises(OverflowError, os.setuid, 1<<32)
-
-        if hasattr(os, 'setgid'):
-            def test_setgid(self):
-                if os.getuid() != 0 and not HAVE_WHEEL_GROUP:
-                    self.assertRaises(OSError, os.setgid, 0)
-                self.assertRaises(OverflowError, os.setgid, 1<<32)
-
-        if hasattr(os, 'seteuid'):
-            def test_seteuid(self):
-                if os.getuid() != 0:
-                    self.assertRaises(OSError, os.seteuid, 0)
-                self.assertRaises(OverflowError, os.seteuid, 1<<32)
-
-        if hasattr(os, 'setegid'):
-            def test_setegid(self):
-                if os.getuid() != 0 and not HAVE_WHEEL_GROUP:
-                    self.assertRaises(OSError, os.setegid, 0)
-                self.assertRaises(OverflowError, os.setegid, 1<<32)
-
-        if hasattr(os, 'setreuid'):
-            def test_setreuid(self):
-                if os.getuid() != 0:
-                    self.assertRaises(OSError, os.setreuid, 0, 0)
-                self.assertRaises(OverflowError, os.setreuid, 1<<32, 0)
-                self.assertRaises(OverflowError, os.setreuid, 0, 1<<32)
-
-            def test_setreuid_neg1(self):
-                # Needs to accept -1.  We run this in a subprocess to avoid
-                # altering the test runner's process state (issue8045).
-                subprocess.check_call([
-                        sys.executable, '-c',
-                        'import os,sys;os.setreuid(-1,-1);sys.exit(0)'])
-
-        if hasattr(os, 'setregid'):
-            def test_setregid(self):
-                if os.getuid() != 0 and not HAVE_WHEEL_GROUP:
-                    self.assertRaises(OSError, os.setregid, 0, 0)
-                self.assertRaises(OverflowError, os.setregid, 1<<32, 0)
-                self.assertRaises(OverflowError, os.setregid, 0, 1<<32)
-
-            def test_setregid_neg1(self):
-                # Needs to accept -1.  We run this in a subprocess to avoid
-                # altering the test runner's process state (issue8045).
-                subprocess.check_call([
-                        sys.executable, '-c',
-                        'import os,sys;os.setregid(-1,-1);sys.exit(0)'])
-
-    class Pep383Tests(unittest.TestCase):
-        def setUp(self):
-            if support.TESTFN_UNENCODABLE:
-                self.dir = support.TESTFN_UNENCODABLE
-            elif support.TESTFN_NONASCII:
-                self.dir = support.TESTFN_NONASCII
-            else:
-                self.dir = support.TESTFN
-            self.bdir = os.fsencode(self.dir)
+@unittest.skipIf(sys.platform == "win32", "Posix specific tests")
+class PosixUidGidTests(unittest.TestCase):
+    @unittest.skipUnless(hasattr(os, 'setuid'), 'test needs os.setuid()')
+    def test_setuid(self):
+        if os.getuid() != 0:
+            self.assertRaises(OSError, os.setuid, 0)
+        self.assertRaises(OverflowError, os.setuid, 1<<32)
+
+    @unittest.skipUnless(hasattr(os, 'setgid'), 'test needs os.setgid()')
+    def test_setgid(self):
+        if os.getuid() != 0 and not HAVE_WHEEL_GROUP:
+            self.assertRaises(OSError, os.setgid, 0)
+        self.assertRaises(OverflowError, os.setgid, 1<<32)
+
+    @unittest.skipUnless(hasattr(os, 'seteuid'), 'test needs os.seteuid()')
+    def test_seteuid(self):
+        if os.getuid() != 0:
+            self.assertRaises(OSError, os.seteuid, 0)
+        self.assertRaises(OverflowError, os.seteuid, 1<<32)
+
+    @unittest.skipUnless(hasattr(os, 'setegid'), 'test needs os.setegid()')
+    def test_setegid(self):
+        if os.getuid() != 0 and not HAVE_WHEEL_GROUP:
+            self.assertRaises(OSError, os.setegid, 0)
+        self.assertRaises(OverflowError, os.setegid, 1<<32)
+
+    @unittest.skipUnless(hasattr(os, 'setreuid'), 'test needs os.setreuid()')
+    def test_setreuid(self):
+        if os.getuid() != 0:
+            self.assertRaises(OSError, os.setreuid, 0, 0)
+        self.assertRaises(OverflowError, os.setreuid, 1<<32, 0)
+        self.assertRaises(OverflowError, os.setreuid, 0, 1<<32)
+
+    @unittest.skipUnless(hasattr(os, 'setreuid'), 'test needs os.setreuid()')
+    def test_setreuid_neg1(self):
+        # Needs to accept -1.  We run this in a subprocess to avoid
+        # altering the test runner's process state (issue8045).
+        subprocess.check_call([
+                sys.executable, '-c',
+                'import os,sys;os.setreuid(-1,-1);sys.exit(0)'])
+
+    @unittest.skipUnless(hasattr(os, 'setregid'), 'test needs os.setregid()')
+    def test_setregid(self):
+        if os.getuid() != 0 and not HAVE_WHEEL_GROUP:
+            self.assertRaises(OSError, os.setregid, 0, 0)
+        self.assertRaises(OverflowError, os.setregid, 1<<32, 0)
+        self.assertRaises(OverflowError, os.setregid, 0, 1<<32)
+
+    @unittest.skipUnless(hasattr(os, 'setregid'), 'test needs os.setregid()')
+    def test_setregid_neg1(self):
+        # Needs to accept -1.  We run this in a subprocess to avoid
+        # altering the test runner's process state (issue8045).
+        subprocess.check_call([
+                sys.executable, '-c',
+                'import os,sys;os.setregid(-1,-1);sys.exit(0)'])
+
+@unittest.skipIf(sys.platform == "win32", "Posix specific tests")
+class Pep383Tests(unittest.TestCase):
+    def setUp(self):
+        if support.TESTFN_UNENCODABLE:
+            self.dir = support.TESTFN_UNENCODABLE
+        elif support.TESTFN_NONASCII:
+            self.dir = support.TESTFN_NONASCII
+        else:
+            self.dir = support.TESTFN
+        self.bdir = os.fsencode(self.dir)
 
-            bytesfn = []
-            def add_filename(fn):
-                try:
-                    fn = os.fsencode(fn)
-                except UnicodeEncodeError:
-                    return
-                bytesfn.append(fn)
-            add_filename(support.TESTFN_UNICODE)
-            if support.TESTFN_UNENCODABLE:
-                add_filename(support.TESTFN_UNENCODABLE)
-            if support.TESTFN_NONASCII:
-                add_filename(support.TESTFN_NONASCII)
-            if not bytesfn:
-                self.skipTest("couldn't create any non-ascii filename")
-
-            self.unicodefn = set()
-            os.mkdir(self.dir)
+        bytesfn = []
+        def add_filename(fn):
             try:
-                for fn in bytesfn:
-                    support.create_empty_file(os.path.join(self.bdir, fn))
-                    fn = os.fsdecode(fn)
-                    if fn in self.unicodefn:
-                        raise ValueError("duplicate filename")
-                    self.unicodefn.add(fn)
-            except:
-                shutil.rmtree(self.dir)
-                raise
-
-        def tearDown(self):
+                fn = os.fsencode(fn)
+            except UnicodeEncodeError:
+                return
+            bytesfn.append(fn)
+        add_filename(support.TESTFN_UNICODE)
+        if support.TESTFN_UNENCODABLE:
+            add_filename(support.TESTFN_UNENCODABLE)
+        if support.TESTFN_NONASCII:
+            add_filename(support.TESTFN_NONASCII)
+        if not bytesfn:
+            self.skipTest("couldn't create any non-ascii filename")
+
+        self.unicodefn = set()
+        os.mkdir(self.dir)
+        try:
+            for fn in bytesfn:
+                support.create_empty_file(os.path.join(self.bdir, fn))
+                fn = os.fsdecode(fn)
+                if fn in self.unicodefn:
+                    raise ValueError("duplicate filename")
+                self.unicodefn.add(fn)
+        except:
             shutil.rmtree(self.dir)
+            raise
 
-        def test_listdir(self):
-            expected = self.unicodefn
-            found = set(os.listdir(self.dir))
-            self.assertEqual(found, expected)
-            # test listdir without arguments
-            current_directory = os.getcwd()
-            try:
-                os.chdir(os.sep)
-                self.assertEqual(set(os.listdir()), set(os.listdir(os.sep)))
-            finally:
-                os.chdir(current_directory)
-
-        def test_open(self):
-            for fn in self.unicodefn:
-                f = open(os.path.join(self.dir, fn), 'rb')
-                f.close()
-
-        @unittest.skipUnless(hasattr(os, 'statvfs'),
-                             "need os.statvfs()")
-        def test_statvfs(self):
-            # issue #9645
-            for fn in self.unicodefn:
-                # should not fail with file not found error
-                fullname = os.path.join(self.dir, fn)
-                os.statvfs(fullname)
-
-        def test_stat(self):
-            for fn in self.unicodefn:
-                os.stat(os.path.join(self.dir, fn))
-else:
-    class PosixUidGidTests(unittest.TestCase):
-        pass
-    class Pep383Tests(unittest.TestCase):
-        pass
+    def tearDown(self):
+        shutil.rmtree(self.dir)
+
+    def test_listdir(self):
+        expected = self.unicodefn
+        found = set(os.listdir(self.dir))
+        self.assertEqual(found, expected)
+        # test listdir without arguments
+        current_directory = os.getcwd()
+        try:
+            os.chdir(os.sep)
+            self.assertEqual(set(os.listdir()), set(os.listdir(os.sep)))
+        finally:
+            os.chdir(current_directory)
+
+    def test_open(self):
+        for fn in self.unicodefn:
+            f = open(os.path.join(self.dir, fn), 'rb')
+            f.close()
+
+    @unittest.skipUnless(hasattr(os, 'statvfs'),
+                            "need os.statvfs()")
+    def test_statvfs(self):
+        # issue #9645
+        for fn in self.unicodefn:
+            # should not fail with file not found error
+            fullname = os.path.join(self.dir, fn)
+            os.statvfs(fullname)
+
+    def test_stat(self):
+        for fn in self.unicodefn:
+            os.stat(os.path.join(self.dir, fn))
 
 @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
 class Win32KillTests(unittest.TestCase):
@@ -1924,6 +1923,8 @@ class TestSendfile(unittest.TestCase):
     SUPPORT_HEADERS_TRAILERS = not sys.platform.startswith("linux") and \
                                not sys.platform.startswith("solaris") and \
                                not sys.platform.startswith("sunos")
+    requires_headers_trailers = unittest.skipUnless(SUPPORT_HEADERS_TRAILERS,
+            'requires headers and trailers support')
 
     @classmethod
     def setUpClass(cls):
@@ -2042,52 +2043,54 @@ class TestSendfile(unittest.TestCase):
 
     # --- headers / trailers tests
 
-    if SUPPORT_HEADERS_TRAILERS:
-
-        def test_headers(self):
-            total_sent = 0
-            sent = os.sendfile(self.sockno, self.fileno, 0, 4096,
-                               headers=[b"x" * 512])
+    @requires_headers_trailers
+    def test_headers(self):
+        total_sent = 0
+        sent = os.sendfile(self.sockno, self.fileno, 0, 4096,
+                            headers=[b"x" * 512])
+        total_sent += sent
+        offset = 4096
+        nbytes = 4096
+        while 1:
+            sent = self.sendfile_wrapper(self.sockno, self.fileno,
+                                                    offset, nbytes)
+            if sent == 0:
+                break
             total_sent += sent
-            offset = 4096
-            nbytes = 4096
-            while 1:
-                sent = self.sendfile_wrapper(self.sockno, self.fileno,
-                                                     offset, nbytes)
-                if sent == 0:
-                    break
-                total_sent += sent
-                offset += sent
+            offset += sent
 
-            expected_data = b"x" * 512 + self.DATA
-            self.assertEqual(total_sent, len(expected_data))
+        expected_data = b"x" * 512 + self.DATA
+        self.assertEqual(total_sent, len(expected_data))
+        self.client.close()
+        self.server.wait()
+        data = self.server.handler_instance.get_data()
+        self.assertEqual(hash(data), hash(expected_data))
+
+    @requires_headers_trailers
+    def test_trailers(self):
+        TESTFN2 = support.TESTFN + "2"
+        file_data = b"abcdef"
+        with open(TESTFN2, 'wb') as f:
+            f.write(file_data)
+        with open(TESTFN2, 'rb')as f:
+            self.addCleanup(os.remove, TESTFN2)
+            os.sendfile(self.sockno, f.fileno(), 0, len(file_data),
+                        trailers=[b"1234"])
             self.client.close()
             self.server.wait()
             data = self.server.handler_instance.get_data()
-            self.assertEqual(hash(data), hash(expected_data))
-
-        def test_trailers(self):
-            TESTFN2 = support.TESTFN + "2"
-            file_data = b"abcdef"
-            with open(TESTFN2, 'wb') as f:
-                f.write(file_data)
-            with open(TESTFN2, 'rb')as f:
-                self.addCleanup(os.remove, TESTFN2)
-                os.sendfile(self.sockno, f.fileno(), 0, len(file_data),
-                            trailers=[b"1234"])
-                self.client.close()
-                self.server.wait()
-                data = self.server.handler_instance.get_data()
-                self.assertEqual(data, b"abcdef1234")
-
-        if hasattr(os, "SF_NODISKIO"):
-            def test_flags(self):
-                try:
-                    os.sendfile(self.sockno, self.fileno, 0, 4096,
-                                flags=os.SF_NODISKIO)
-                except OSError as err:
-                    if err.errno not in (errno.EBUSY, errno.EAGAIN):
-                        raise
+            self.assertEqual(data, b"abcdef1234")
+
+    @requires_headers_trailers
+    @unittest.skipUnless(hasattr(os, 'SF_NODISKIO'),
+                         'test needs os.SF_NODISKIO')
+    def test_flags(self):
+        try:
+            os.sendfile(self.sockno, self.fileno, 0, 4096,
+                        flags=os.SF_NODISKIO)
+        except OSError as err:
+            if err.errno not in (errno.EBUSY, errno.EAGAIN):
+                raise
 
 
 def supports_extended_attributes():
diff --git a/Lib/test/test_poplib.py b/Lib/test/test_poplib.py
index dd51ac99d7..70fe4265c5 100644
--- a/Lib/test/test_poplib.py
+++ b/Lib/test/test_poplib.py
@@ -11,7 +11,7 @@ import os
 import time
 import errno
 
-from unittest import TestCase
+from unittest import TestCase, skipUnless
 from test import support as test_support
 threading = test_support.import_module('threading')
 
@@ -24,6 +24,7 @@ if hasattr(poplib, 'POP3_SSL'):
 
     SUPPORTS_SSL = True
     CERTFILE = os.path.join(os.path.dirname(__file__) or os.curdir, "keycert.pem")
+requires_ssl = skipUnless(SUPPORTS_SSL, 'SSL not supported')
 
 # the dummy data returned by server when LIST and RETR commands are issued
 LIST_RESP = b'1 1\r\n2 2\r\n3 3\r\n4 4\r\n5 5\r\n.\r\n'
@@ -316,22 +317,23 @@ class TestPOP3Class(TestCase):
         self.assertIsNone(self.client.sock)
         self.assertIsNone(self.client.file)
 
-    if SUPPORTS_SSL:
-
-        def test_stls_capa(self):
-            capa = self.client.capa()
-            self.assertTrue('STLS' in capa.keys())
+    @requires_ssl
+    def test_stls_capa(self):
+        capa = self.client.capa()
+        self.assertTrue('STLS' in capa.keys())
 
-        def test_stls(self):
-            expected = b'+OK Begin TLS negotiation'
-            resp = self.client.stls()
-            self.assertEqual(resp, expected)
+    @requires_ssl
+    def test_stls(self):
+        expected = b'+OK Begin TLS negotiation'
+        resp = self.client.stls()
+        self.assertEqual(resp, expected)
 
-        def test_stls_context(self):
-            expected = b'+OK Begin TLS negotiation'
-            ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
-            resp = self.client.stls(context=ctx)
-            self.assertEqual(resp, expected)
+    @requires_ssl
+    def test_stls_context(self):
+        expected = b'+OK Begin TLS negotiation'
+        ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
+        resp = self.client.stls(context=ctx)
+        self.assertEqual(resp, expected)
 
 
 if SUPPORTS_SSL:
@@ -354,73 +356,75 @@ if SUPPORTS_SSL:
             self.push('+OK dummy pop3 server ready. <timestamp>')
 
 
-    class TestPOP3_SSLClass(TestPOP3Class):
-        # repeat previous tests by using poplib.POP3_SSL
-
-        def setUp(self):
-            self.server = DummyPOP3Server((HOST, PORT))
-            self.server.handler = DummyPOP3_SSLHandler
-            self.server.start()
-            self.client = poplib.POP3_SSL(self.server.host, self.server.port)
-
-        def test__all__(self):
-            self.assertIn('POP3_SSL', poplib.__all__)
-
-        def test_context(self):
-            ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
-            self.assertRaises(ValueError, poplib.POP3_SSL, self.server.host,
-                              self.server.port, keyfile=CERTFILE, context=ctx)
-            self.assertRaises(ValueError, poplib.POP3_SSL, self.server.host,
-                              self.server.port, certfile=CERTFILE, context=ctx)
-            self.assertRaises(ValueError, poplib.POP3_SSL, self.server.host,
-                              self.server.port, keyfile=CERTFILE,
-                              certfile=CERTFILE, context=ctx)
+@requires_ssl
+class TestPOP3_SSLClass(TestPOP3Class):
+    # repeat previous tests by using poplib.POP3_SSL
 
-            self.client.quit()
-            self.client = poplib.POP3_SSL(self.server.host, self.server.port,
-                                          context=ctx)
-            self.assertIsInstance(self.client.sock, ssl.SSLSocket)
-            self.assertIs(self.client.sock.context, ctx)
-            self.assertTrue(self.client.noop().startswith(b'+OK'))
-
-        def test_stls(self):
-            self.assertRaises(poplib.error_proto, self.client.stls)
-
-        test_stls_context = test_stls
-
-        def test_stls_capa(self):
-            capa = self.client.capa()
-            self.assertFalse('STLS' in capa.keys())
+    def setUp(self):
+        self.server = DummyPOP3Server((HOST, PORT))
+        self.server.handler = DummyPOP3_SSLHandler
+        self.server.start()
+        self.client = poplib.POP3_SSL(self.server.host, self.server.port)
+
+    def test__all__(self):
+        self.assertIn('POP3_SSL', poplib.__all__)
+
+    def test_context(self):
+        ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
+        self.assertRaises(ValueError, poplib.POP3_SSL, self.server.host,
+                            self.server.port, keyfile=CERTFILE, context=ctx)
+        self.assertRaises(ValueError, poplib.POP3_SSL, self.server.host,
+                            self.server.port, certfile=CERTFILE, context=ctx)
+        self.assertRaises(ValueError, poplib.POP3_SSL, self.server.host,
+                            self.server.port, keyfile=CERTFILE,
+                            certfile=CERTFILE, context=ctx)
+
+        self.client.quit()
+        self.client = poplib.POP3_SSL(self.server.host, self.server.port,
+                                        context=ctx)
+        self.assertIsInstance(self.client.sock, ssl.SSLSocket)
+        self.assertIs(self.client.sock.context, ctx)
+        self.assertTrue(self.client.noop().startswith(b'+OK'))
+
+    def test_stls(self):
+        self.assertRaises(poplib.error_proto, self.client.stls)
+
+    test_stls_context = test_stls
+
+    def test_stls_capa(self):
+        capa = self.client.capa()
+        self.assertFalse('STLS' in capa.keys())
 
 
-    class TestPOP3_TLSClass(TestPOP3Class):
-        # repeat previous tests by using poplib.POP3.stls()
+@requires_ssl
+class TestPOP3_TLSClass(TestPOP3Class):
+    # repeat previous tests by using poplib.POP3.stls()
 
-        def setUp(self):
-            self.server = DummyPOP3Server((HOST, PORT))
-            self.server.start()
-            self.client = poplib.POP3(self.server.host, self.server.port, timeout=3)
-            self.client.stls()
+    def setUp(self):
+        self.server = DummyPOP3Server((HOST, PORT))
+        self.server.start()
+        self.client = poplib.POP3(self.server.host, self.server.port, timeout=3)
+        self.client.stls()
 
-        def tearDown(self):
-            if self.client.file is not None and self.client.sock is not None:
-                try:
-                    self.client.quit()
-                except poplib.error_proto:
-                    # happens in the test_too_long_lines case; the overlong
-                    # response will be treated as response to QUIT and raise
-                    # this exception
-                    pass
-            self.server.stop()
+    def tearDown(self):
+        if self.client.file is not None and self.client.sock is not None:
+            try:
+                self.client.quit()
+            except poplib.error_proto:
+                # happens in the test_too_long_lines case; the overlong
+                # response will be treated as response to QUIT and raise
+                # this exception
+                pass
+        self.server.stop()
 
-        def test_stls(self):
-            self.assertRaises(poplib.error_proto, self.client.stls)
+    def test_stls(self):
+        self.assertRaises(poplib.error_proto, self.client.stls)
 
-        test_stls_context = test_stls
+    test_stls_context = test_stls
 
-        def test_stls_capa(self):
-            capa = self.client.capa()
-            self.assertFalse(b'STLS' in capa.keys())
+    def test_stls_capa(self):
+        capa = self.client.capa()
+        self.assertFalse(b'STLS' in capa.keys())
 
 
 class TestTimeouts(TestCase):
@@ -478,10 +482,8 @@ class TestTimeouts(TestCase):
 
 
 def test_main():
-    tests = [TestPOP3Class, TestTimeouts]
-    if SUPPORTS_SSL:
-        tests.append(TestPOP3_SSLClass)
-        tests.append(TestPOP3_TLSClass)
+    tests = [TestPOP3Class, TestTimeouts,
+             TestPOP3_SSLClass, TestPOP3_TLSClass]
     thread_info = test_support.threading_setup()
     try:
         test_support.run_unittest(*tests)
diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index 6cd3393a63..1eceebe7ac 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -54,47 +54,55 @@ class PosixTester(unittest.TestCase):
                 posix_func()
                 self.assertRaises(TypeError, posix_func, 1)
 
-    if hasattr(posix, 'getresuid'):
-        def test_getresuid(self):
-            user_ids = posix.getresuid()
-            self.assertEqual(len(user_ids), 3)
-            for val in user_ids:
-                self.assertGreaterEqual(val, 0)
-
-    if hasattr(posix, 'getresgid'):
-        def test_getresgid(self):
-            group_ids = posix.getresgid()
-            self.assertEqual(len(group_ids), 3)
-            for val in group_ids:
-                self.assertGreaterEqual(val, 0)
-
-    if hasattr(posix, 'setresuid'):
-        def test_setresuid(self):
-            current_user_ids = posix.getresuid()
-            self.assertIsNone(posix.setresuid(*current_user_ids))
-            # -1 means don't change that value.
-            self.assertIsNone(posix.setresuid(-1, -1, -1))
-
-        def test_setresuid_exception(self):
-            # Don't do this test if someone is silly enough to run us as root.
-            current_user_ids = posix.getresuid()
-            if 0 not in current_user_ids:
-                new_user_ids = (current_user_ids[0]+1, -1, -1)
-                self.assertRaises(OSError, posix.setresuid, *new_user_ids)
-
-    if hasattr(posix, 'setresgid'):
-        def test_setresgid(self):
-            current_group_ids = posix.getresgid()
-            self.assertIsNone(posix.setresgid(*current_group_ids))
-            # -1 means don't change that value.
-            self.assertIsNone(posix.setresgid(-1, -1, -1))
-
-        def test_setresgid_exception(self):
-            # Don't do this test if someone is silly enough to run us as root.
-            current_group_ids = posix.getresgid()
-            if 0 not in current_group_ids:
-                new_group_ids = (current_group_ids[0]+1, -1, -1)
-                self.assertRaises(OSError, posix.setresgid, *new_group_ids)
+    @unittest.skipUnless(hasattr(posix, 'getresuid'),
+                         'test needs posix.getresuid()')
+    def test_getresuid(self):
+        user_ids = posix.getresuid()
+        self.assertEqual(len(user_ids), 3)
+        for val in user_ids:
+            self.assertGreaterEqual(val, 0)
+
+    @unittest.skipUnless(hasattr(posix, 'getresgid'),
+                         'test needs posix.getresgid()')
+    def test_getresgid(self):
+        group_ids = posix.getresgid()
+        self.assertEqual(len(group_ids), 3)
+        for val in group_ids:
+            self.assertGreaterEqual(val, 0)
+
+    @unittest.skipUnless(hasattr(posix, 'setresuid'),
+                         'test needs posix.setresuid()')
+    def test_setresuid(self):
+        current_user_ids = posix.getresuid()
+        self.assertIsNone(posix.setresuid(*current_user_ids))
+        # -1 means don't change that value.
+        self.assertIsNone(posix.setresuid(-1, -1, -1))
+
+    @unittest.skipUnless(hasattr(posix, 'setresuid'),
+                         'test needs posix.setresuid()')
+    def test_setresuid_exception(self):
+        # Don't do this test if someone is silly enough to run us as root.
+        current_user_ids = posix.getresuid()
+        if 0 not in current_user_ids:
+            new_user_ids = (current_user_ids[0]+1, -1, -1)
+            self.assertRaises(OSError, posix.setresuid, *new_user_ids)
+
+    @unittest.skipUnless(hasattr(posix, 'setresgid'),
+                         'test needs posix.setresgid()')
+    def test_setresgid(self):
+        current_group_ids = posix.getresgid()
+        self.assertIsNone(posix.setresgid(*current_group_ids))
+        # -1 means don't change that value.
+        self.assertIsNone(posix.setresgid(-1, -1, -1))
+
+    @unittest.skipUnless(hasattr(posix, 'setresgid'),
+                         'test needs posix.setresgid()')
+    def test_setresgid_exception(self):
+        # Don't do this test if someone is silly enough to run us as root.
+        current_group_ids = posix.getresgid()
+        if 0 not in current_group_ids:
+            new_group_ids = (current_group_ids[0]+1, -1, -1)
+            self.assertRaises(OSError, posix.setresgid, *new_group_ids)
 
     @unittest.skipUnless(hasattr(posix, 'initgroups'),
                          "test needs os.initgroups()")
@@ -121,29 +129,32 @@ class PosixTester(unittest.TestCase):
             else:
                 self.fail("Expected OSError to be raised by initgroups")
 
+    @unittest.skipUnless(hasattr(posix, 'statvfs'),
+                         'test needs posix.statvfs()')
     def test_statvfs(self):
-        if hasattr(posix, 'statvfs'):
-            self.assertTrue(posix.statvfs(os.curdir))
+        self.assertTrue(posix.statvfs(os.curdir))
 
+    @unittest.skipUnless(hasattr(posix, 'fstatvfs'),
+                         'test needs posix.fstatvfs()')
     def test_fstatvfs(self):
-        if hasattr(posix, 'fstatvfs'):
-            fp = open(support.TESTFN)
-            try:
-                self.assertTrue(posix.fstatvfs(fp.fileno()))
-                self.assertTrue(posix.statvfs(fp.fileno()))
-            finally:
-                fp.close()
+        fp = open(support.TESTFN)
+        try:
+            self.assertTrue(posix.fstatvfs(fp.fileno()))
+            self.assertTrue(posix.statvfs(fp.fileno()))
+        finally:
+            fp.close()
 
+    @unittest.skipUnless(hasattr(posix, 'ftruncate'),
+                         'test needs posix.ftruncate()')
     def test_ftruncate(self):
-        if hasattr(posix, 'ftruncate'):
-            fp = open(support.TESTFN, 'w+')
-            try:
-                # we need to have some data to truncate
-                fp.write('test')
-                fp.flush()
-                posix.ftruncate(fp.fileno(), 0)
-            finally:
-                fp.close()
+        fp = open(support.TESTFN, 'w+')
+        try:
+            # we need to have some data to truncate
+            fp.write('test')
+            fp.flush()
+            posix.ftruncate(fp.fileno(), 0)
+        finally:
+            fp.close()
 
     @unittest.skipUnless(hasattr(posix, 'truncate'), "test needs posix.truncate()")
     def test_truncate(self):
@@ -290,30 +301,33 @@ class PosixTester(unittest.TestCase):
         finally:
             os.close(fd)
 
+    @unittest.skipUnless(hasattr(posix, 'dup'),
+                         'test needs posix.dup()')
     def test_dup(self):
-        if hasattr(posix, 'dup'):
-            fp = open(support.TESTFN)
-            try:
-                fd = posix.dup(fp.fileno())
-                self.assertIsInstance(fd, int)
-                os.close(fd)
-            finally:
-                fp.close()
+        fp = open(support.TESTFN)
+        try:
+            fd = posix.dup(fp.fileno())
+            self.assertIsInstance(fd, int)
+            os.close(fd)
+        finally:
+            fp.close()
 
+    @unittest.skipUnless(hasattr(posix, 'confstr'),
+                         'test needs posix.confstr()')
     def test_confstr(self):
-        if hasattr(posix, 'confstr'):
-            self.assertRaises(ValueError, posix.confstr, "CS_garbage")
-            self.assertEqual(len(posix.confstr("CS_PATH")) > 0, True)
+        self.assertRaises(ValueError, posix.confstr, "CS_garbage")
+        self.assertEqual(len(posix.confstr("CS_PATH")) > 0, True)
 
+    @unittest.skipUnless(hasattr(posix, 'dup2'),
+                         'test needs posix.dup2()')
     def test_dup2(self):
-        if hasattr(posix, 'dup2'):
-            fp1 = open(support.TESTFN)
-            fp2 = open(support.TESTFN)
-            try:
-                posix.dup2(fp1.fileno(), fp2.fileno())
-            finally:
-                fp1.close()
-                fp2.close()
+        fp1 = open(support.TESTFN)
+        fp2 = open(support.TESTFN)
+        try:
+            posix.dup2(fp1.fileno(), fp2.fileno())
+        finally:
+            fp1.close()
+            fp2.close()
 
     @unittest.skipUnless(hasattr(os, 'O_CLOEXEC'), "needs os.O_CLOEXEC")
     @support.requires_linux_version(2, 6, 23)
@@ -322,65 +336,69 @@ class PosixTester(unittest.TestCase):
         self.addCleanup(os.close, fd)
         self.assertTrue(fcntl.fcntl(fd, fcntl.F_GETFD) & fcntl.FD_CLOEXEC)
 
+    @unittest.skipUnless(hasattr(posix, 'O_EXLOCK'),
+                         'test needs posix.O_EXLOCK')
     def test_osexlock(self):
-        if hasattr(posix, "O_EXLOCK"):
+        fd = os.open(support.TESTFN,
+                     os.O_WRONLY|os.O_EXLOCK|os.O_CREAT)
+        self.assertRaises(OSError, os.open, support.TESTFN,
+                          os.O_WRONLY|os.O_EXLOCK|os.O_NONBLOCK)
+        os.close(fd)
+
+        if hasattr(posix, "O_SHLOCK"):
             fd = os.open(support.TESTFN,
-                         os.O_WRONLY|os.O_EXLOCK|os.O_CREAT)
+                         os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
             self.assertRaises(OSError, os.open, support.TESTFN,
                               os.O_WRONLY|os.O_EXLOCK|os.O_NONBLOCK)
             os.close(fd)
 
-            if hasattr(posix, "O_SHLOCK"):
-                fd = os.open(support.TESTFN,
-                             os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
-                self.assertRaises(OSError, os.open, support.TESTFN,
-                                  os.O_WRONLY|os.O_EXLOCK|os.O_NONBLOCK)
-                os.close(fd)
-
+    @unittest.skipUnless(hasattr(posix, 'O_SHLOCK'),
+                         'test needs posix.O_SHLOCK')
     def test_osshlock(self):
-        if hasattr(posix, "O_SHLOCK"):
-            fd1 = os.open(support.TESTFN,
+        fd1 = os.open(support.TESTFN,
+                     os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
+        fd2 = os.open(support.TESTFN,
+                      os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
+        os.close(fd2)
+        os.close(fd1)
+
+        if hasattr(posix, "O_EXLOCK"):
+            fd = os.open(support.TESTFN,
                          os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
-            fd2 = os.open(support.TESTFN,
-                          os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
-            os.close(fd2)
-            os.close(fd1)
-
-            if hasattr(posix, "O_EXLOCK"):
-                fd = os.open(support.TESTFN,
-                             os.O_WRONLY|os.O_SHLOCK|os.O_CREAT)
-                self.assertRaises(OSError, os.open, support.TESTFN,
-                                  os.O_RDONLY|os.O_EXLOCK|os.O_NONBLOCK)
-                os.close(fd)
+            self.assertRaises(OSError, os.open, support.TESTFN,
+                              os.O_RDONLY|os.O_EXLOCK|os.O_NONBLOCK)
+            os.close(fd)
 
+    @unittest.skipUnless(hasattr(posix, 'fstat'),
+                         'test needs posix.fstat()')
     def test_fstat(self):
-        if hasattr(posix, 'fstat'):
-            fp = open(support.TESTFN)
-            try:
-                self.assertTrue(posix.fstat(fp.fileno()))
-                self.assertTrue(posix.stat(fp.fileno()))
-
-                self.assertRaisesRegex(TypeError,
-                        'should be string, bytes or integer, not',
-                        posix.stat, float(fp.fileno()))
-            finally:
-                fp.close()
-
-    def test_stat(self):
-        if hasattr(posix, 'stat'):
-            self.assertTrue(posix.stat(support.TESTFN))
-            self.assertTrue(posix.stat(os.fsencode(support.TESTFN)))
-            self.assertTrue(posix.stat(bytearray(os.fsencode(support.TESTFN))))
+        fp = open(support.TESTFN)
+        try:
+            self.assertTrue(posix.fstat(fp.fileno()))
+            self.assertTrue(posix.stat(fp.fileno()))
 
             self.assertRaisesRegex(TypeError,
-                    'can\'t specify None for path argument',
-                    posix.stat, None)
-            self.assertRaisesRegex(TypeError,
-                    'should be string, bytes or integer, not',
-                    posix.stat, list(support.TESTFN))
-            self.assertRaisesRegex(TypeError,
                     'should be string, bytes or integer, not',
-                    posix.stat, list(os.fsencode(support.TESTFN)))
+                    posix.stat, float(fp.fileno()))
+        finally:
+            fp.close()
+
+    @unittest.skipUnless(hasattr(posix, 'stat'),
+                         'test needs posix.stat()')
+    def test_stat(self):
+        self.assertTrue(posix.stat(support.TESTFN))
+        self.assertTrue(posix.stat(os.fsencode(support.TESTFN)))
+        self.assertTrue(posix.stat(bytearray(os.fsencode(support.TESTFN))))
+
+        self.assertRaisesRegex(TypeError,
+                'can\'t specify None for path argument',
+                posix.stat, None)
+        self.assertRaisesRegex(TypeError,
+                'should be string, bytes or integer, not',
+                posix.stat, list(support.TESTFN))
+        self.assertRaisesRegex(TypeError,
+                'should be string, bytes or integer, not',
+                posix.stat, list(os.fsencode(support.TESTFN)))
 
     @unittest.skipUnless(hasattr(posix, 'mkfifo'), "don't have mkfifo()")
     def test_mkfifo(self):
@@ -495,10 +513,10 @@ class PosixTester(unittest.TestCase):
         self._test_all_chown_common(posix.lchown, support.TESTFN,
                                     getattr(posix, 'lstat', None))
 
+    @unittest.skipUnless(hasattr(posix, 'chdir'), 'test needs posix.chdir()')
     def test_chdir(self):
-        if hasattr(posix, 'chdir'):
-            posix.chdir(os.curdir)
-            self.assertRaises(OSError, posix.chdir, support.TESTFN)
+        posix.chdir(os.curdir)
+        self.assertRaises(OSError, posix.chdir, support.TESTFN)
 
     def test_listdir(self):
         self.assertTrue(support.TESTFN in posix.listdir(os.curdir))
@@ -528,25 +546,26 @@ class PosixTester(unittest.TestCase):
             sorted(posix.listdir(f))
             )
 
+    @unittest.skipUnless(hasattr(posix, 'access'), 'test needs posix.access()')
     def test_access(self):
-        if hasattr(posix, 'access'):
-            self.assertTrue(posix.access(support.TESTFN, os.R_OK))
+        self.assertTrue(posix.access(support.TESTFN, os.R_OK))
 
+    @unittest.skipUnless(hasattr(posix, 'umask'), 'test needs posix.umask()')
     def test_umask(self):
-        if hasattr(posix, 'umask'):
-            old_mask = posix.umask(0)
-            self.assertIsInstance(old_mask, int)
-            posix.umask(old_mask)
+        old_mask = posix.umask(0)
+        self.assertIsInstance(old_mask, int)
+        posix.umask(old_mask)
 
+    @unittest.skipUnless(hasattr(posix, 'strerror'),
+                         'test needs posix.strerror()')
     def test_strerror(self):
-        if hasattr(posix, 'strerror'):
-            self.assertTrue(posix.strerror(0))
+        self.assertTrue(posix.strerror(0))
 
+    @unittest.skipUnless(hasattr(posix, 'pipe'), 'test needs posix.pipe()')
     def test_pipe(self):
-        if hasattr(posix, 'pipe'):
-            reader, writer = posix.pipe()
-            os.close(reader)
-            os.close(writer)
+        reader, writer = posix.pipe()
+        os.close(reader)
+        os.close(writer)
 
     @unittest.skipUnless(hasattr(os, 'pipe2'), "test needs os.pipe2()")
     @support.requires_linux_version(2, 6, 27)
@@ -580,15 +599,15 @@ class PosixTester(unittest.TestCase):
         self.assertRaises(OverflowError, os.pipe2, _testcapi.INT_MAX + 1)
         self.assertRaises(OverflowError, os.pipe2, _testcapi.UINT_MAX + 1)
 
+    @unittest.skipUnless(hasattr(posix, 'utime'), 'test needs posix.utime()')
     def test_utime(self):
-        if hasattr(posix, 'utime'):
-            now = time.time()
-            posix.utime(support.TESTFN, None)
-            self.assertRaises(TypeError, posix.utime, support.TESTFN, (None, None))
-            self.assertRaises(TypeError, posix.utime, support.TESTFN, (now, None))
-            self.assertRaises(TypeError, posix.utime, support.TESTFN, (None, now))
-            posix.utime(support.TESTFN, (int(now), int(now)))
-            posix.utime(support.TESTFN, (now, now))
+        now = time.time()
+        posix.utime(support.TESTFN, None)
+        self.assertRaises(TypeError, posix.utime, support.TESTFN, (None, None))
+        self.assertRaises(TypeError, posix.utime, support.TESTFN, (now, None))
+        self.assertRaises(TypeError, posix.utime, support.TESTFN, (None, now))
+        posix.utime(support.TESTFN, (int(now), int(now)))
+        posix.utime(support.TESTFN, (now, now))
 
     def _test_chflags_regular_file(self, chflags_func, target_file, **kwargs):
         st = os.stat(target_file)
@@ -665,6 +684,7 @@ class PosixTester(unittest.TestCase):
             self.assertEqual(type(k), item_type)
             self.assertEqual(type(v), item_type)
 
+    @unittest.skipUnless(hasattr(posix, 'getcwd'), 'test needs posix.getcwd()')
     def test_getcwd_long_pathnames(self):
         dirname = 'getcwd-test-directory-0123456789abcdef-01234567890abcdef'
         curdir = os.getcwd()
diff --git a/Lib/test/test_set.py b/Lib/test/test_set.py
index 13cefec1a9..bfef621093 100644
--- a/Lib/test/test_set.py
+++ b/Lib/test/test_set.py
@@ -625,10 +625,10 @@ class TestSet(TestJointOps, unittest.TestCase):
         myset >= myobj
         self.assertTrue(myobj.le_called)
 
-    # C API test only available in a debug build
-    if hasattr(set, "test_c_api"):
-        def test_c_api(self):
-            self.assertEqual(set().test_c_api(), True)
+    @unittest.skipUnless(hasattr(set, "test_c_api"),
+                         'C API test only available in a debug build')
+    def test_c_api(self):
+        self.assertEqual(set().test_c_api(), True)
 
 class SetSubclass(set):
     pass
diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py
index 0fbe078dbf..deb1577611 100644
--- a/Lib/test/test_shutil.py
+++ b/Lib/test/test_shutil.py
@@ -195,37 +195,37 @@ class TestShutil(unittest.TestCase):
         self.assertIn(errors[1][2][1].filename, possible_args)
 
 
-    # See bug #1071513 for why we don't run this on cygwin
-    # and bug #1076467 for why we don't run this as root.
-    if (hasattr(os, 'chmod') and sys.platform[:6] != 'cygwin'
-        and not (hasattr(os, 'geteuid') and os.geteuid() == 0)):
-        def test_on_error(self):
-            self.errorState = 0
-            os.mkdir(TESTFN)
-            self.addCleanup(shutil.rmtree, TESTFN)
-
-            self.child_file_path = os.path.join(TESTFN, 'a')
-            self.child_dir_path = os.path.join(TESTFN, 'b')
-            support.create_empty_file(self.child_file_path)
-            os.mkdir(self.child_dir_path)
-            old_dir_mode = os.stat(TESTFN).st_mode
-            old_child_file_mode = os.stat(self.child_file_path).st_mode
-            old_child_dir_mode = os.stat(self.child_dir_path).st_mode
-            # Make unwritable.
-            new_mode = stat.S_IREAD|stat.S_IEXEC
-            os.chmod(self.child_file_path, new_mode)
-            os.chmod(self.child_dir_path, new_mode)
-            os.chmod(TESTFN, new_mode)
-
-            self.addCleanup(os.chmod, TESTFN, old_dir_mode)
-            self.addCleanup(os.chmod, self.child_file_path, old_child_file_mode)
-            self.addCleanup(os.chmod, self.child_dir_path, old_child_dir_mode)
-
-            shutil.rmtree(TESTFN, onerror=self.check_args_to_onerror)
-            # Test whether onerror has actually been called.
-            self.assertEqual(self.errorState, 3,
-                             "Expected call to onerror function did not "
-                             "happen.")
+    @unittest.skipUnless(hasattr(os, 'chmod'), 'requires os.chmod()')
+    @unittest.skipIf(sys.platform[:6] == 'cygwin',
+                     "This test can't be run on Cygwin (issue #1071513).")
+    @unittest.skipIf(hasattr(os, 'geteuid') and os.geteuid() == 0,
+                     "This test can't be run reliably as root (issue #1076467).")
+    def test_on_error(self):
+        self.errorState = 0
+        os.mkdir(TESTFN)
+        self.addCleanup(shutil.rmtree, TESTFN)
+
+        self.child_file_path = os.path.join(TESTFN, 'a')
+        self.child_dir_path = os.path.join(TESTFN, 'b')
+        support.create_empty_file(self.child_file_path)
+        os.mkdir(self.child_dir_path)
+        old_dir_mode = os.stat(TESTFN).st_mode
+        old_child_file_mode = os.stat(self.child_file_path).st_mode
+        old_child_dir_mode = os.stat(self.child_dir_path).st_mode
+        # Make unwritable.
+        new_mode = stat.S_IREAD|stat.S_IEXEC
+        os.chmod(self.child_file_path, new_mode)
+        os.chmod(self.child_dir_path, new_mode)
+        os.chmod(TESTFN, new_mode)
+
+        self.addCleanup(os.chmod, TESTFN, old_dir_mode)
+        self.addCleanup(os.chmod, self.child_file_path, old_child_file_mode)
+        self.addCleanup(os.chmod, self.child_dir_path, old_child_dir_mode)
+
+        shutil.rmtree(TESTFN, onerror=self.check_args_to_onerror)
+        # Test whether onerror has actually been called.
+        self.assertEqual(self.errorState, 3,
+                         "Expected call to onerror function did not happen.")
 
     def check_args_to_onerror(self, func, arg, exc):
         # test_rmtree_errors deliberately runs rmtree
@@ -807,38 +807,39 @@ class TestShutil(unittest.TestCase):
         finally:
             shutil.rmtree(TESTFN, ignore_errors=True)
 
-    if hasattr(os, "mkfifo"):
-        # Issue #3002: copyfile and copytree block indefinitely on named pipes
-        def test_copyfile_named_pipe(self):
-            os.mkfifo(TESTFN)
-            try:
-                self.assertRaises(shutil.SpecialFileError,
-                                  shutil.copyfile, TESTFN, TESTFN2)
-                self.assertRaises(shutil.SpecialFileError,
-                                  shutil.copyfile, __file__, TESTFN)
-            finally:
-                os.remove(TESTFN)
+    # Issue #3002: copyfile and copytree block indefinitely on named pipes
+    @unittest.skipUnless(hasattr(os, "mkfifo"), 'requires os.mkfifo()')
+    def test_copyfile_named_pipe(self):
+        os.mkfifo(TESTFN)
+        try:
+            self.assertRaises(shutil.SpecialFileError,
+                                shutil.copyfile, TESTFN, TESTFN2)
+            self.assertRaises(shutil.SpecialFileError,
+                                shutil.copyfile, __file__, TESTFN)
+        finally:
+            os.remove(TESTFN)
 
-        @support.skip_unless_symlink
-        def test_copytree_named_pipe(self):
-            os.mkdir(TESTFN)
+    @unittest.skipUnless(hasattr(os, "mkfifo"), 'requires os.mkfifo()')
+    @support.skip_unless_symlink
+    def test_copytree_named_pipe(self):
+        os.mkdir(TESTFN)
+        try:
+            subdir = os.path.join(TESTFN, "subdir")
+            os.mkdir(subdir)
+            pipe = os.path.join(subdir, "mypipe")
+            os.mkfifo(pipe)
             try:
-                subdir = os.path.join(TESTFN, "subdir")
-                os.mkdir(subdir)
-                pipe = os.path.join(subdir, "mypipe")
-                os.mkfifo(pipe)
-                try:
-                    shutil.copytree(TESTFN, TESTFN2)
-                except shutil.Error as e:
-                    errors = e.args[0]
-                    self.assertEqual(len(errors), 1)
-                    src, dst, error_msg = errors[0]
-                    self.assertEqual("`%s` is a named pipe" % pipe, error_msg)
-                else:
-                    self.fail("shutil.Error should have been raised")
-            finally:
-                shutil.rmtree(TESTFN, ignore_errors=True)
-                shutil.rmtree(TESTFN2, ignore_errors=True)
+                shutil.copytree(TESTFN, TESTFN2)
+            except shutil.Error as e:
+                errors = e.args[0]
+                self.assertEqual(len(errors), 1)
+                src, dst, error_msg = errors[0]
+                self.assertEqual("`%s` is a named pipe" % pipe, error_msg)
+            else:
+                self.fail("shutil.Error should have been raised")
+        finally:
+            shutil.rmtree(TESTFN, ignore_errors=True)
+            shutil.rmtree(TESTFN2, ignore_errors=True)
 
     def test_copytree_special_func(self):
 
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index e995c99df1..beff31a7f5 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -817,16 +817,17 @@ class GeneralModuleTests(unittest.TestCase):
         self.assertRaises(TypeError, socket.if_nametoindex, 0)
         self.assertRaises(TypeError, socket.if_indextoname, '_DEADBEEF')
 
+    @unittest.skipUnless(hasattr(sys, 'getrefcount'),
+                         'test needs sys.getrefcount()')
     def testRefCountGetNameInfo(self):
         # Testing reference count for getnameinfo
-        if hasattr(sys, "getrefcount"):
-            try:
-                # On some versions, this loses a reference
-                orig = sys.getrefcount(__name__)
-                socket.getnameinfo(__name__,0)
-            except TypeError:
-                if sys.getrefcount(__name__) != orig:
-                    self.fail("socket.getnameinfo loses a reference")
+        try:
+            # On some versions, this loses a reference
+            orig = sys.getrefcount(__name__)
+            socket.getnameinfo(__name__,0)
+        except TypeError:
+            if sys.getrefcount(__name__) != orig:
+                self.fail("socket.getnameinfo loses a reference")
 
     def testInterpreterCrash(self):
         # Making sure getnameinfo doesn't crash the interpreter
@@ -931,17 +932,17 @@ class GeneralModuleTests(unittest.TestCase):
         # Check that setting it to an invalid type raises TypeError
         self.assertRaises(TypeError, socket.setdefaulttimeout, "spam")
 
+    @unittest.skipUnless(hasattr(socket, 'inet_aton'),
+                         'test needs socket.inet_aton()')
     def testIPv4_inet_aton_fourbytes(self):
-        if not hasattr(socket, 'inet_aton'):
-            return  # No inet_aton, nothing to check
         # Test that issue1008086 and issue767150 are fixed.
         # It must return 4 bytes.
         self.assertEqual(b'\x00'*4, socket.inet_aton('0.0.0.0'))
         self.assertEqual(b'\xff'*4, socket.inet_aton('255.255.255.255'))
 
+    @unittest.skipUnless(hasattr(socket, 'inet_pton'),
+                         'test needs socket.inet_pton()')
     def testIPv4toString(self):
-        if not hasattr(socket, 'inet_pton'):
-            return # No inet_pton() on this platform
         from socket import inet_aton as f, inet_pton, AF_INET
         g = lambda a: inet_pton(AF_INET, a)
 
@@ -970,9 +971,9 @@ class GeneralModuleTests(unittest.TestCase):
         assertInvalid(g, '1.2.3.4.5')
         assertInvalid(g, '::1')
 
+    @unittest.skipUnless(hasattr(socket, 'inet_pton'),
+                         'test needs socket.inet_pton()')
     def testIPv6toString(self):
-        if not hasattr(socket, 'inet_pton'):
-            return # No inet_pton() on this platform
         try:
             from socket import inet_pton, AF_INET6, has_ipv6
             if not has_ipv6:
@@ -1024,9 +1025,9 @@ class GeneralModuleTests(unittest.TestCase):
         assertInvalid('::1.2.3.4:0')
         assertInvalid('0.100.200.0:3:4:5:6:7:8')
 
+    @unittest.skipUnless(hasattr(socket, 'inet_ntop'),
+                         'test needs socket.inet_ntop()')
     def testStringToIPv4(self):
-        if not hasattr(socket, 'inet_ntop'):
-            return # No inet_ntop() on this platform
         from socket import inet_ntoa as f, inet_ntop, AF_INET
         g = lambda a: inet_ntop(AF_INET, a)
         assertInvalid = lambda func,a: self.assertRaises(
@@ -1048,9 +1049,9 @@ class GeneralModuleTests(unittest.TestCase):
         assertInvalid(g, b'\x00' * 5)
         assertInvalid(g, b'\x00' * 16)
 
+    @unittest.skipUnless(hasattr(socket, 'inet_ntop'),
+                         'test needs socket.inet_ntop()')
     def testStringToIPv6(self):
-        if not hasattr(socket, 'inet_ntop'):
-            return # No inet_ntop() on this platform
         try:
             from socket import inet_ntop, AF_INET6, has_ipv6
             if not has_ipv6:
@@ -3660,6 +3661,8 @@ class TCPCloserTest(ThreadedTCPSocketTest):
         self.cli.connect((HOST, self.port))
         time.sleep(1.0)
 
+@unittest.skipUnless(hasattr(socket, 'socketpair'),
+                     'test needs socket.socketpair()')
 @unittest.skipUnless(thread, 'Threading required for this test.')
 class BasicSocketPairTest(SocketPairTest):
 
@@ -3722,26 +3725,27 @@ class NonBlockingTCPTests(ThreadedTCPSocketTest):
     def _testSetBlocking(self):
         pass
 
-    if hasattr(socket, "SOCK_NONBLOCK"):
-        @support.requires_linux_version(2, 6, 28)
-        def testInitNonBlocking(self):
-            # reinit server socket
-            self.serv.close()
-            self.serv = socket.socket(socket.AF_INET, socket.SOCK_STREAM |
-                                                      socket.SOCK_NONBLOCK)
-            self.port = support.bind_port(self.serv)
-            self.serv.listen(1)
-            # actual testing
-            start = time.time()
-            try:
-                self.serv.accept()
-            except OSError:
-                pass
-            end = time.time()
-            self.assertTrue((end - start) < 1.0, "Error creating with non-blocking mode.")
-
-        def _testInitNonBlocking(self):
+    @unittest.skipUnless(hasattr(socket, 'SOCK_NONBLOCK'),
+                         'test needs socket.SOCK_NONBLOCK')
+    @support.requires_linux_version(2, 6, 28)
+    def testInitNonBlocking(self):
+        # reinit server socket
+        self.serv.close()
+        self.serv = socket.socket(socket.AF_INET, socket.SOCK_STREAM |
+                                                  socket.SOCK_NONBLOCK)
+        self.port = support.bind_port(self.serv)
+        self.serv.listen(1)
+        # actual testing
+        start = time.time()
+        try:
+            self.serv.accept()
+        except OSError:
             pass
+        end = time.time()
+        self.assertTrue((end - start) < 1.0, "Error creating with non-blocking mode.")
+
+    def _testInitNonBlocking(self):
+        pass
 
     def testInheritFlags(self):
         # Issue #7995: when calling accept() on a listening socket with a
@@ -4431,12 +4435,12 @@ class TCPTimeoutTest(SocketTCPTest):
         if not ok:
             self.fail("accept() returned success when we did not expect it")
 
+    @unittest.skipUnless(hasattr(signal, 'alarm'),
+                         'test needs signal.alarm()')
     def testInterruptedTimeout(self):
         # XXX I don't know how to do this test on MSWindows or any other
         # plaform that doesn't support signal.alarm() or os.kill(), though
         # the bug should have existed on all platforms.
-        if not hasattr(signal, "alarm"):
-            return                  # can only test on *nix
         self.serv.settimeout(5.0)   # must be longer than alarm
         class Alarm(Exception):
             pass
@@ -4496,6 +4500,7 @@ class TestExceptions(unittest.TestCase):
         self.assertTrue(issubclass(socket.gaierror, OSError))
         self.assertTrue(issubclass(socket.timeout, OSError))
 
+@unittest.skipUnless(sys.platform == 'linux', 'Linux specific test')
 class TestLinuxAbstractNamespace(unittest.TestCase):
 
     UNIX_PATH_MAX = 108
@@ -4531,6 +4536,7 @@ class TestLinuxAbstractNamespace(unittest.TestCase):
         finally:
             s.close()
 
+@unittest.skipUnless(hasattr(socket, 'AF_UNIX'), 'test needs socket.AF_UNIX')
 class TestUnixDomain(unittest.TestCase):
 
     def setUp(self):
@@ -4680,10 +4686,10 @@ def isTipcAvailable():
         for line in f:
             if line.startswith("tipc "):
                 return True
-    if support.verbose:
-        print("TIPC module is not loaded, please 'sudo modprobe tipc'")
     return False
 
+@unittest.skipUnless(isTipcAvailable(),
+                     "TIPC module is not loaded, please 'sudo modprobe tipc'")
 class TIPCTest(unittest.TestCase):
     def testRDM(self):
         srv = socket.socket(socket.AF_TIPC, socket.SOCK_RDM)
@@ -4706,6 +4712,8 @@ class TIPCTest(unittest.TestCase):
         self.assertEqual(msg, MSG)
 
 
+@unittest.skipUnless(isTipcAvailable(),
+                     "TIPC module is not loaded, please 'sudo modprobe tipc'")
 class TIPCThreadableTest(unittest.TestCase, ThreadableTest):
     def __init__(self, methodName = 'runTest'):
         unittest.TestCase.__init__(self, methodName = methodName)
@@ -5028,15 +5036,10 @@ def test_main():
         InheritanceTest,
         NonblockConstantTest
     ])
-    if hasattr(socket, "socketpair"):
-        tests.append(BasicSocketPairTest)
-    if hasattr(socket, "AF_UNIX"):
-        tests.append(TestUnixDomain)
-    if sys.platform == 'linux':
-        tests.append(TestLinuxAbstractNamespace)
-    if isTipcAvailable():
-        tests.append(TIPCTest)
-        tests.append(TIPCThreadableTest)
+    tests.append(BasicSocketPairTest)
+    tests.append(TestUnixDomain)
+    tests.append(TestLinuxAbstractNamespace)
+    tests.extend([TIPCTest, TIPCThreadableTest])
     tests.extend([BasicCANTest, CANTest])
     tests.extend([BasicRDSTest, RDSTest])
     tests.extend([
diff --git a/Lib/test/test_socketserver.py b/Lib/test/test_socketserver.py
index 02c6c1e4fd..0617b30a69 100644
--- a/Lib/test/test_socketserver.py
+++ b/Lib/test/test_socketserver.py
@@ -27,7 +27,10 @@ TEST_STR = b"hello world\n"
 HOST = test.support.HOST
 
 HAVE_UNIX_SOCKETS = hasattr(socket, "AF_UNIX")
+requires_unix_sockets = unittest.skipUnless(HAVE_UNIX_SOCKETS,
+                                            'requires Unix sockets')
 HAVE_FORKING = hasattr(os, "fork")
+requires_forking = unittest.skipUnless(HAVE_FORKING, 'requires forking')
 
 def signal_alarm(n):
     """Call signal.alarm when it exists (i.e. not on Windows)."""
@@ -175,31 +178,33 @@ class SocketServerTest(unittest.TestCase):
                         socketserver.StreamRequestHandler,
                         self.stream_examine)
 
-    if HAVE_FORKING:
-        def test_ForkingTCPServer(self):
-            with simple_subprocess(self):
-                self.run_server(socketserver.ForkingTCPServer,
-                                socketserver.StreamRequestHandler,
-                                self.stream_examine)
-
-    if HAVE_UNIX_SOCKETS:
-        def test_UnixStreamServer(self):
-            self.run_server(socketserver.UnixStreamServer,
+    @requires_forking
+    def test_ForkingTCPServer(self):
+        with simple_subprocess(self):
+            self.run_server(socketserver.ForkingTCPServer,
                             socketserver.StreamRequestHandler,
                             self.stream_examine)
 
-        def test_ThreadingUnixStreamServer(self):
-            self.run_server(socketserver.ThreadingUnixStreamServer,
+    @requires_unix_sockets
+    def test_UnixStreamServer(self):
+        self.run_server(socketserver.UnixStreamServer,
+                        socketserver.StreamRequestHandler,
+                        self.stream_examine)
+
+    @requires_unix_sockets
+    def test_ThreadingUnixStreamServer(self):
+        self.run_server(socketserver.ThreadingUnixStreamServer,
+                        socketserver.StreamRequestHandler,
+                        self.stream_examine)
+
+    @requires_unix_sockets
+    @requires_forking
+    def test_ForkingUnixStreamServer(self):
+        with simple_subprocess(self):
+            self.run_server(ForkingUnixStreamServer,
                             socketserver.StreamRequestHandler,
                             self.stream_examine)
 
-        if HAVE_FORKING:
-            def test_ForkingUnixStreamServer(self):
-                with simple_subprocess(self):
-                    self.run_server(ForkingUnixStreamServer,
-                                    socketserver.StreamRequestHandler,
-                                    self.stream_examine)
-
     def test_UDPServer(self):
         self.run_server(socketserver.UDPServer,
                         socketserver.DatagramRequestHandler,
@@ -210,12 +215,12 @@ class SocketServerTest(unittest.TestCase):
                         socketserver.DatagramRequestHandler,
                         self.dgram_examine)
 
-    if HAVE_FORKING:
-        def test_ForkingUDPServer(self):
-            with simple_subprocess(self):
-                self.run_server(socketserver.ForkingUDPServer,
-                                socketserver.DatagramRequestHandler,
-                                self.dgram_examine)
+    @requires_forking
+    def test_ForkingUDPServer(self):
+        with simple_subprocess(self):
+            self.run_server(socketserver.ForkingUDPServer,
+                            socketserver.DatagramRequestHandler,
+                            self.dgram_examine)
 
     @contextlib.contextmanager
     def mocked_select_module(self):
@@ -252,22 +257,24 @@ class SocketServerTest(unittest.TestCase):
     # Alas, on Linux (at least) recvfrom() doesn't return a meaningful
     # client address so this cannot work:
 
-    # if HAVE_UNIX_SOCKETS:
-    #     def test_UnixDatagramServer(self):
-    #         self.run_server(socketserver.UnixDatagramServer,
-    #                         socketserver.DatagramRequestHandler,
-    #                         self.dgram_examine)
+    # @requires_unix_sockets
+    # def test_UnixDatagramServer(self):
+    #     self.run_server(socketserver.UnixDatagramServer,
+    #                     socketserver.DatagramRequestHandler,
+    #                     self.dgram_examine)
     #
-    #     def test_ThreadingUnixDatagramServer(self):
-    #         self.run_server(socketserver.ThreadingUnixDatagramServer,
-    #                         socketserver.DatagramRequestHandler,
-    #                         self.dgram_examine)
+    # @requires_unix_sockets
+    # def test_ThreadingUnixDatagramServer(self):
+    #     self.run_server(socketserver.ThreadingUnixDatagramServer,
+    #                     socketserver.DatagramRequestHandler,
+    #                     self.dgram_examine)
     #
-    #     if HAVE_FORKING:
-    #         def test_ForkingUnixDatagramServer(self):
-    #             self.run_server(socketserver.ForkingUnixDatagramServer,
-    #                             socketserver.DatagramRequestHandler,
-    #                             self.dgram_examine)
+    # @requires_unix_sockets
+    # @requires_forking
+    # def test_ForkingUnixDatagramServer(self):
+    #     self.run_server(socketserver.ForkingUnixDatagramServer,
+    #                     socketserver.DatagramRequestHandler,
+    #                     self.dgram_examine)
 
     @reap_threads
     def test_shutdown(self):
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 8437745cb9..0565f39e2c 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -293,15 +293,16 @@ class SysModuleTest(unittest.TestCase):
     def test_call_tracing(self):
         self.assertRaises(TypeError, sys.call_tracing, type, 2)
 
+    @unittest.skipUnless(hasattr(sys, "setdlopenflags"),
+                         'test needs sys.setdlopenflags()')
     def test_dlopenflags(self):
-        if hasattr(sys, "setdlopenflags"):
-            self.assertTrue(hasattr(sys, "getdlopenflags"))
-            self.assertRaises(TypeError, sys.getdlopenflags, 42)
-            oldflags = sys.getdlopenflags()
-            self.assertRaises(TypeError, sys.setdlopenflags)
-            sys.setdlopenflags(oldflags+1)
-            self.assertEqual(sys.getdlopenflags(), oldflags+1)
-            sys.setdlopenflags(oldflags)
+        self.assertTrue(hasattr(sys, "getdlopenflags"))
+        self.assertRaises(TypeError, sys.getdlopenflags, 42)
+        oldflags = sys.getdlopenflags()
+        self.assertRaises(TypeError, sys.setdlopenflags)
+        sys.setdlopenflags(oldflags+1)
+        self.assertEqual(sys.getdlopenflags(), oldflags+1)
+        sys.setdlopenflags(oldflags)
 
     @test.support.refcount_test
     def test_refcount(self):
diff --git a/Lib/test/test_warnings.py b/Lib/test/test_warnings.py
index 13c7df1cb2..87463ac1a3 100644
--- a/Lib/test/test_warnings.py
+++ b/Lib/test/test_warnings.py
@@ -271,11 +271,10 @@ class WarnTests(BaseTest):
         finally:
             warning_tests.__file__ = filename
 
+    @unittest.skipUnless(hasattr(sys, 'argv'), 'test needs sys.argv')
     def test_missing_filename_main_with_argv(self):
         # If __file__ is not specified and the caller is __main__ and sys.argv
         # exists, then use sys.argv[0] as the file.
-        if not hasattr(sys, 'argv'):
-            return
         filename = warning_tests.__file__
         module_name = warning_tests.__name__
         try:
diff --git a/Lib/test/test_zlib.py b/Lib/test/test_zlib.py
index 2f6f84042f..1daa8f8a7e 100644
--- a/Lib/test/test_zlib.py
+++ b/Lib/test/test_zlib.py
@@ -7,6 +7,13 @@ from test.support import bigmemtest, _1G, _4G
 
 zlib = support.import_module('zlib')
 
+requires_Compress_copy = unittest.skipUnless(
+        hasattr(zlib.compressobj(), "copy"),
+        'requires Compress.copy()')
+requires_Decompress_copy = unittest.skipUnless(
+        hasattr(zlib.decompressobj(), "copy"),
+        'requires Decompress.copy()')
+
 
 class VersionTestCase(unittest.TestCase):
 
@@ -381,39 +388,39 @@ class CompressObjectTestCase(BaseCompressTestCase, unittest.TestCase):
                                         "mode=%i, level=%i") % (sync, level))
                 del obj
 
+    @unittest.skipUnless(hasattr(zlib, 'Z_SYNC_FLUSH'),
+                         'requires zlib.Z_SYNC_FLUSH')
     def test_odd_flush(self):
         # Test for odd flushing bugs noted in 2.0, and hopefully fixed in 2.1
         import random
+        # Testing on 17K of "random" data
 
-        if hasattr(zlib, 'Z_SYNC_FLUSH'):
-            # Testing on 17K of "random" data
-
-            # Create compressor and decompressor objects
-            co = zlib.compressobj(zlib.Z_BEST_COMPRESSION)
-            dco = zlib.decompressobj()
+        # Create compressor and decompressor objects
+        co = zlib.compressobj(zlib.Z_BEST_COMPRESSION)
+        dco = zlib.decompressobj()
 
-            # Try 17K of data
-            # generate random data stream
+        # Try 17K of data
+        # generate random data stream
+        try:
+            # In 2.3 and later, WichmannHill is the RNG of the bug report
+            gen = random.WichmannHill()
+        except AttributeError:
             try:
-                # In 2.3 and later, WichmannHill is the RNG of the bug report
-                gen = random.WichmannHill()
+                # 2.2 called it Random
+                gen = random.Random()
             except AttributeError:
-                try:
-                    # 2.2 called it Random
-                    gen = random.Random()
-                except AttributeError:
-                    # others might simply have a single RNG
-                    gen = random
-            gen.seed(1)
-            data = genblock(1, 17 * 1024, generator=gen)
-
-            # compress, sync-flush, and decompress
-            first = co.compress(data)
-            second = co.flush(zlib.Z_SYNC_FLUSH)
-            expanded = dco.decompress(first + second)
-
-            # if decompressed data is different from the input data, choke.
-            self.assertEqual(expanded, data, "17K random source doesn't match")
+                # others might simply have a single RNG
+                gen = random
+        gen.seed(1)
+        data = genblock(1, 17 * 1024, generator=gen)
+
+        # compress, sync-flush, and decompress
+        first = co.compress(data)
+        second = co.flush(zlib.Z_SYNC_FLUSH)
+        expanded = dco.decompress(first + second)
+
+        # if decompressed data is different from the input data, choke.
+        self.assertEqual(expanded, data, "17K random source doesn't match")
 
     def test_empty_flush(self):
         # Test that calling .flush() on unused objects works.
@@ -525,67 +532,69 @@ class CompressObjectTestCase(BaseCompressTestCase, unittest.TestCase):
         data = zlib.compress(input2)
         self.assertEqual(dco.flush(), input1[1:])
 
-    if hasattr(zlib.compressobj(), "copy"):
-        def test_compresscopy(self):
-            # Test copying a compression object
-            data0 = HAMLET_SCENE
-            data1 = bytes(str(HAMLET_SCENE, "ascii").swapcase(), "ascii")
-            c0 = zlib.compressobj(zlib.Z_BEST_COMPRESSION)
-            bufs0 = []
-            bufs0.append(c0.compress(data0))
-
-            c1 = c0.copy()
-            bufs1 = bufs0[:]
-
-            bufs0.append(c0.compress(data0))
-            bufs0.append(c0.flush())
-            s0 = b''.join(bufs0)
-
-            bufs1.append(c1.compress(data1))
-            bufs1.append(c1.flush())
-            s1 = b''.join(bufs1)
-
-            self.assertEqual(zlib.decompress(s0),data0+data0)
-            self.assertEqual(zlib.decompress(s1),data0+data1)
-
-        def test_badcompresscopy(self):
-            # Test copying a compression object in an inconsistent state
-            c = zlib.compressobj()
-            c.compress(HAMLET_SCENE)
-            c.flush()
-            self.assertRaises(ValueError, c.copy)
-
-    if hasattr(zlib.decompressobj(), "copy"):
-        def test_decompresscopy(self):
-            # Test copying a decompression object
-            data = HAMLET_SCENE
-            comp = zlib.compress(data)
-            # Test type of return value
-            self.assertIsInstance(comp, bytes)
-
-            d0 = zlib.decompressobj()
-            bufs0 = []
-            bufs0.append(d0.decompress(comp[:32]))
-
-            d1 = d0.copy()
-            bufs1 = bufs0[:]
-
-            bufs0.append(d0.decompress(comp[32:]))
-            s0 = b''.join(bufs0)
-
-            bufs1.append(d1.decompress(comp[32:]))
-            s1 = b''.join(bufs1)
-
-            self.assertEqual(s0,s1)
-            self.assertEqual(s0,data)
-
-        def test_baddecompresscopy(self):
-            # Test copying a compression object in an inconsistent state
-            data = zlib.compress(HAMLET_SCENE)
-            d = zlib.decompressobj()
-            d.decompress(data)
-            d.flush()
-            self.assertRaises(ValueError, d.copy)
+    @requires_Compress_copy
+    def test_compresscopy(self):
+        # Test copying a compression object
+        data0 = HAMLET_SCENE
+        data1 = bytes(str(HAMLET_SCENE, "ascii").swapcase(), "ascii")
+        c0 = zlib.compressobj(zlib.Z_BEST_COMPRESSION)
+        bufs0 = []
+        bufs0.append(c0.compress(data0))
+
+        c1 = c0.copy()
+        bufs1 = bufs0[:]
+
+        bufs0.append(c0.compress(data0))
+        bufs0.append(c0.flush())
+        s0 = b''.join(bufs0)
+
+        bufs1.append(c1.compress(data1))
+        bufs1.append(c1.flush())
+        s1 = b''.join(bufs1)
+
+        self.assertEqual(zlib.decompress(s0),data0+data0)
+        self.assertEqual(zlib.decompress(s1),data0+data1)
+
+    @requires_Compress_copy
+    def test_badcompresscopy(self):
+        # Test copying a compression object in an inconsistent state
+        c = zlib.compressobj()
+        c.compress(HAMLET_SCENE)
+        c.flush()
+        self.assertRaises(ValueError, c.copy)
+
+    @requires_Decompress_copy
+    def test_decompresscopy(self):
+        # Test copying a decompression object
+        data = HAMLET_SCENE
+        comp = zlib.compress(data)
+        # Test type of return value
+        self.assertIsInstance(comp, bytes)
+
+        d0 = zlib.decompressobj()
+        bufs0 = []
+        bufs0.append(d0.decompress(comp[:32]))
+
+        d1 = d0.copy()
+        bufs1 = bufs0[:]
+
+        bufs0.append(d0.decompress(comp[32:]))
+        s0 = b''.join(bufs0)
+
+        bufs1.append(d1.decompress(comp[32:]))
+        s1 = b''.join(bufs1)
+
+        self.assertEqual(s0,s1)
+        self.assertEqual(s0,data)
+
+    @requires_Decompress_copy
+    def test_baddecompresscopy(self):
+        # Test copying a compression object in an inconsistent state
+        data = zlib.compress(HAMLET_SCENE)
+        d = zlib.decompressobj()
+        d.decompress(data)
+        d.flush()
+        self.assertRaises(ValueError, d.copy)
 
     # Memory use of the following functions takes into account overallocation