Issue #7849: Now the utility ``check_warnings`` verifies if the warnings are

effectively raised.  A new utility ``check_py3k_warnings`` deals with py3k warnings.

Lib/test/string_tests.py

@@ -715,8 +715,7 @@ class CommonTest(unittest.TestCase):
         EQ("bobobXbobob", "bobobobXbobobob", "replace", "bobob", "bob")
         EQ("BOBOBOB", "BOBOBOB", "replace", "bob", "bobby")
 
-        # Silence Py3k warning
-        with test_support.check_warnings():
+        with test_support.check_py3k_warnings():
             ba = buffer('a')
             bb = buffer('b')
         EQ("bbc", "abc", "replace", ba, bb)

Lib/test/test_ascii_formatd.py

@@ -17,14 +17,11 @@ class FormatDeprecationTests(unittest.TestCase):
         PyOS_ascii_formatd = pythonapi.PyOS_ascii_formatd
         buf = create_string_buffer(' ' * 100)
 
-        with check_warnings() as w:
-            warnings.simplefilter('default')
+        with check_warnings():
             PyOS_ascii_formatd(byref(buf), sizeof(buf), '%+.10f',
                                c_double(10.0))
             self.assertEqual(buf.value, '+10.0000000000')
 
-        self.assertEqual(w.category, DeprecationWarning)
-
 class FormatTests(unittest.TestCase):
     # ensure that, for the restricted set of format codes,
     # %-formatting returns the same values os PyOS_ascii_formatd

Lib/test/test_fileio.py

@@ -390,7 +390,7 @@ class OtherFileTests(unittest.TestCase):
         self.assertRaises(TypeError, _FileIO, "1", 0, 0)
 
     def testWarnings(self):
-        with check_warnings() as w:
+        with check_warnings(quiet=True) as w:
             self.assertEqual(w.warnings, [])
             self.assertRaises(TypeError, _FileIO, [])
             self.assertEqual(w.warnings, [])

Lib/test/test_index.py

@@ -279,16 +279,14 @@ class OverflowTestCase(unittest.TestCase):
 
     def test_getitem(self):
         self._getitem_helper(object)
-        # Silence Py3k warning
-        with test_support.check_warnings():
+        with test_support.check_py3k_warnings():
             self._getslice_helper_deprecated(object)
 
     def test_getitem_classic(self):
         class Empty: pass
         # XXX This test fails (see bug #7532)
         #self._getitem_helper(Empty)
-        # Silence Py3k warning
-        with test_support.check_warnings():
+        with test_support.check_py3k_warnings():
             self._getslice_helper_deprecated(Empty)
 
     def test_sequence_repeat(self):
@@ -308,8 +306,7 @@ def test_main():
         XRangeTestCase,
         OverflowTestCase,
     )
-    # Silence Py3k warning
-    with test_support.check_warnings():
+    with test_support.check_py3k_warnings():
         test_support.run_unittest(
             ClassicSeqDeprecatedTestCase,
             NewSeqDeprecatedTestCase,

Lib/test/test_random.py

@@ -53,8 +53,7 @@ class TestBasicOps(unittest.TestCase):
         state3 = self.gen.getstate()    # s/b distinct from state2
         self.assertNotEqual(state2, state3)
 
-        # Silence py3k warnings
-        with test_support.check_warnings():
+        with test_support.check_py3k_warnings(quiet=True):
             self.assertRaises(TypeError, self.gen.jumpahead)  # needs an arg
             self.assertRaises(TypeError, self.gen.jumpahead, "ick")  # wrong type
             self.assertRaises(TypeError, self.gen.jumpahead, 2.3)  # wrong type

Lib/test/test_support.py

@@ -16,6 +16,7 @@ import warnings
 import unittest
 import importlib
 import UserDict
+import re
 
 __all__ = ["Error", "TestFailed", "ResourceDenied", "import_module",
            "verbose", "use_resources", "max_memuse", "record_original_stdout",
@@ -23,8 +24,8 @@ __all__ = ["Error", "TestFailed", "ResourceDenied", "import_module",
            "is_resource_enabled", "requires", "find_unused_port", "bind_port",
            "fcmp", "have_unicode", "is_jython", "TESTFN", "HOST", "FUZZ",
            "SAVEDCWD", "temp_cwd", "findfile", "sortdict", "check_syntax_error",
-           "open_urlresource", "check_warnings", "CleanImport",
-           "EnvironmentVarGuard", "captured_output",
+           "open_urlresource", "check_warnings", "check_py3k_warnings",
+           "CleanImport", "EnvironmentVarGuard", "captured_output",
            "captured_stdout", "TransientResource", "transient_internet",
            "run_with_locale", "set_memlimit", "bigmemtest", "bigaddrspacetest",
            "BasicTestRunner", "run_unittest", "run_doctest", "threading_setup",
@@ -488,22 +489,103 @@ class WarningsRecorder(object):
        entry to the warnings.catch_warnings() context manager.
     """
     def __init__(self, warnings_list):
-        self.warnings = warnings_list
+        self._warnings = warnings_list
+        self._last = 0
 
     def __getattr__(self, attr):
-        if self.warnings:
-            return getattr(self.warnings[-1], attr)
+        if len(self._warnings) > self._last:
+            return getattr(self._warnings[-1], attr)
         elif attr in warnings.WarningMessage._WARNING_DETAILS:
             return None
         raise AttributeError("%r has no attribute %r" % (self, attr))
 
+    @property
+    def warnings(self):
+        return self._warnings[self._last:]
+
     def reset(self):
-        del self.warnings[:]
+        self._last = len(self._warnings)
 
-@contextlib.contextmanager
-def check_warnings():
+
+def _filterwarnings(filters, quiet=False):
+    """Catch the warnings, then check if all the expected
+    warnings have been raised and re-raise unexpected warnings.
+    If 'quiet' is True, only re-raise the unexpected warnings.
+    """
+    # Clear the warning registry of the calling module
+    # in order to re-raise the warnings.
+    frame = sys._getframe(2)
+    registry = frame.f_globals.get('__warningregistry__')
+    if registry:
+        registry.clear()
     with warnings.catch_warnings(record=True) as w:
+        # Disable filters, to record all warnings.  Because
+        # test_warnings swap the module, we need to look up
+        # in the sys.modules dictionary.
+        sys.modules['warnings'].resetwarnings()
         yield WarningsRecorder(w)
+    # Filter the recorded warnings
+    reraise = [warning.message for warning in w]
+    missing = []
+    for msg, cat in filters:
+        seen = False
+        for exc in reraise[:]:
+            message = str(exc)
+            # Filter out the matching messages
+            if (re.match(msg, message, re.I) and
+                issubclass(exc.__class__, cat)):
+                seen = True
+                reraise.remove(exc)
+        if not seen and not quiet:
+            # This filter caught nothing
+            missing.append((msg, cat.__name__))
+    for exc in reraise:
+        raise AssertionError("unhandled warning %r" % exc)
+    for filter in missing:
+        raise AssertionError("filter (%r, %s) did not caught any warning" %
+                             filter)
+
+
+@contextlib.contextmanager
+def check_warnings(*filters, **kwargs):
+    """Context manager to silence warnings.
+
+    Accept 2-tuples as positional arguments:
+        ("message regexp", WarningCategory)
+
+    Optional argument:
+     - if 'quiet' is True, it does not fail if a filter catches nothing
+        (default False)
+
+    Without argument, it defaults to:
+        check_warnings(("", Warning), quiet=False)
+    """
+    if not filters:
+        filters = (("", Warning),)
+    return _filterwarnings(filters, kwargs.get('quiet'))
+
+
+@contextlib.contextmanager
+def check_py3k_warnings(*filters, **kwargs):
+    """Context manager to silence py3k warnings.
+
+    Accept 2-tuples as positional arguments:
+        ("message regexp", WarningCategory)
+
+    Optional argument:
+     - if 'quiet' is True, it does not fail if a filter catches nothing
+        (default False)
+
+    Without argument, it defaults to:
+        check_py3k_warnings(("", DeprecationWarning), quiet=False)
+    """
+    if sys.py3kwarning:
+        if not filters:
+            filters = (("", DeprecationWarning),)
+    else:
+        # It should not raise any py3k warning
+        filters = ()
+    return _filterwarnings(filters, kwargs.get('quiet'))
 
 
 class CleanImport(object):
@@ -735,7 +817,6 @@ _4G = 4 * _1G
 MAX_Py_ssize_t = sys.maxsize
 
 def set_memlimit(limit):
-    import re
     global max_memuse
     global real_max_memuse
     sizes = {

Lib/test/test_unicode.py

@@ -512,8 +512,7 @@ class UnicodeTest(
         )
 
         if not sys.platform.startswith('java'):
-            # Silence Py3k warning
-            with test_support.check_warnings():
+            with test_support.check_py3k_warnings():
                 buf = buffer('character buffers are decoded to unicode')
             self.assertEqual(
                 unicode(

Misc/NEWS

@@ -138,6 +138,9 @@ Extension Modules
 Tests
 -----
 
+- Issue #7849: Now the utility ``check_warnings`` verifies if the warnings are
+  effectively raised.  A new utility ``check_py3k_warnings`` is available.
+
 - The four path modules (genericpath, macpath, ntpath, posixpath) share a
   common TestCase for some tests: test_genericpath.CommonTest.