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/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)
+
+
+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():
-    with warnings.catch_warnings(record=True) as w:
-        yield WarningsRecorder(w)
+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 = {