bpo-41003: Fix test_copyreg when numpy is installed (GH-20935)

Fix test_copyreg when numpy is installed: test.pickletester now
saves/restores warnings.filters when importing numpy, to ignore
filters installed by numpy.

Add the save_restore_warnings_filters() function to the
test.support.warnings_helper module.

1 files changed, 11 insertions, 5 deletions

diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index ca566a28d6..a34505aab5 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -21,20 +21,26 @@ try:
 except ImportError:
     _testbuffer = None
 
-try:
-    import numpy as np
-except ImportError:
-    np = None
-
 from test import support
 from test.support import (
     TestFailed, TESTFN, run_with_locale, no_tracing,
     _2G, _4G, bigmemtest, forget,
     )
 from test.support import threading_helper
+from test.support.warnings_helper import save_restore_warnings_filters
 
 from pickle import bytes_types
 
+
+# bpo-41003: Save/restore warnings filters to leave them unchanged.
+# Ignore filters installed by numpy.
+try:
+    with save_restore_warnings_filters():
+        import numpy as np
+except ImportError:
+    np = None
+
+
 requires_32b = unittest.skipUnless(sys.maxsize < 2**32,
                                    "test is only meaningful on 32-bit builds")