dont use exception catches for warnings; modernize xdist detection

Improvements to the test suite's integration with pytest such that the
"warnings" plugin, if manually enabled, will not interfere with the test
suite, such that third parties can enable the warnings plugin or make use
of the ``-W`` parameter and SQLAlchemy's test suite will continue to pass.
Additionally, modernized the detection of the "pytest-xdist" plugin so that
plugins can be globally disabled using PYTEST_DISABLE_PLUGIN_AUTOLOAD=1
without breaking the test suite if xdist were still installed. Warning
filters that promote deprecation warnings to errors are now localized to
SQLAlchemy-specific warnings, or within SQLAlchemy-specific sources for
general Python deprecation warnings, so that non-SQLAlchemy deprecation
warnings emitted from pytest plugins should also not impact the test suite.

Fixes: #7599
Change-Id: Ibcf09af25228d39ee5a943fda82d8a9302433726

1 files changed, 25 insertions, 21 deletions

diff --git a/test/sql/test_metadata.py b/test/sql/test_metadata.py
index 8a9c868be..e02f0e2ed 100644
--- a/test/sql/test_metadata.py
+++ b/test/sql/test_metadata.py
@@ -53,6 +53,7 @@ from sqlalchemy.testing import is_
 from sqlalchemy.testing import is_false
 from sqlalchemy.testing import is_true
 from sqlalchemy.testing import mock
+from sqlalchemy.testing.assertions import expect_warnings
 
 
 class MetaDataTest(fixtures.TestBase, ComparesTables):
@@ -1822,32 +1823,35 @@ class TableTest(fixtures.TestBase, AssertsCompiledSQL):
 
     def test_pk_col_mismatch_one(self):
         m = MetaData()
-        assert_raises_message(
-            exc.SAWarning,
+
+        with expect_warnings(
             "Table 't' specifies columns 'x' as primary_key=True, "
-            "not matching locally specified columns 'q'",
-            Table,
-            "t",
-            m,
-            Column("x", Integer, primary_key=True),
-            Column("q", Integer),
-            PrimaryKeyConstraint("q"),
-        )
+            "not matching locally specified columns 'q'"
+        ):
+            Table(
+                "t",
+                m,
+                Column("x", Integer, primary_key=True),
+                Column("q", Integer),
+                PrimaryKeyConstraint("q"),
+            )
 
     def test_pk_col_mismatch_two(self):
         m = MetaData()
-        assert_raises_message(
-            exc.SAWarning,
+
+        with expect_warnings(
             "Table 't' specifies columns 'a', 'b', 'c' as primary_key=True, "
-            "not matching locally specified columns 'b', 'c'",
-            Table,
-            "t",
-            m,
-            Column("a", Integer, primary_key=True),
-            Column("b", Integer, primary_key=True),
-            Column("c", Integer, primary_key=True),
-            PrimaryKeyConstraint("b", "c"),
-        )
+            "not matching locally specified columns 'b', 'c'"
+        ):
+
+            Table(
+                "t",
+                m,
+                Column("a", Integer, primary_key=True),
+                Column("b", Integer, primary_key=True),
+                Column("c", Integer, primary_key=True),
+                PrimaryKeyConstraint("b", "c"),
+            )
 
     @testing.emits_warning("Table 't'")
     def test_pk_col_mismatch_three(self):