#8155: Preserve backward compatibility for test_support.check_warnings(). Add regression tests.

Lib/test/test_support.py

@@ -577,14 +577,19 @@ def check_warnings(*filters, **kwargs):
 
     Optional argument:
      - if 'quiet' is True, it does not fail if a filter catches nothing
-        (default False)
+        (default True without argument,
+         default False if some filters are defined)
 
     Without argument, it defaults to:
-        check_warnings(("", Warning), quiet=False)
+        check_warnings(("", Warning), quiet=True)
     """
+    quiet = kwargs.get('quiet')
     if not filters:
         filters = (("", Warning),)
-    return _filterwarnings(filters, kwargs.get('quiet'))
+        # Preserve backward compatibility
+        if quiet is None:
+            quiet = True
+    return _filterwarnings(filters, quiet)
 
 
 @contextlib.contextmanager

Lib/test/test_warnings.py

@@ -633,19 +633,33 @@ class CatchWarningTests(BaseTest):
     def test_check_warnings(self):
         # Explicit tests for the test_support convenience wrapper
         wmod = self.module
-        if wmod is sys.modules['warnings']:
-            with test_support.check_warnings() as w:
-                self.assertEqual(w.warnings, [])
-                wmod.simplefilter("always")
-                wmod.warn("foo")
-                self.assertEqual(str(w.message), "foo")
-                wmod.warn("bar")
-                self.assertEqual(str(w.message), "bar")
-                self.assertEqual(str(w.warnings[0].message), "foo")
-                self.assertEqual(str(w.warnings[1].message), "bar")
-                w.reset()
-                self.assertEqual(w.warnings, [])
+        if wmod is not sys.modules['warnings']:
+            return
+        with test_support.check_warnings(quiet=False) as w:
+            self.assertEqual(w.warnings, [])
+            wmod.simplefilter("always")
+            wmod.warn("foo")
+            self.assertEqual(str(w.message), "foo")
+            wmod.warn("bar")
+            self.assertEqual(str(w.message), "bar")
+            self.assertEqual(str(w.warnings[0].message), "foo")
+            self.assertEqual(str(w.warnings[1].message), "bar")
+            w.reset()
+            self.assertEqual(w.warnings, [])
+
+        with test_support.check_warnings():
+            # defaults to quiet=True without argument
+            pass
+        with test_support.check_warnings(('foo', UserWarning)):
+            wmod.warn("foo")
 
+        with self.assertRaises(AssertionError):
+            with test_support.check_warnings(('', RuntimeWarning)):
+                # defaults to quiet=False with argument
+                pass
+        with self.assertRaises(AssertionError):
+            with test_support.check_warnings(('foo', RuntimeWarning)):
+                wmod.warn("foo")
 
 
 class CCatchWarningTests(CatchWarningTests):