Make test.test_support.catch_warnings more robust as discussed on pyt…

…hon-dev. Also add explicit tests for it to test_warnings. (forward port of r64910 from trunk)

Doc/library/test.rst

@@ -211,7 +211,7 @@ This module defines the following exceptions:
    Subclass of :exc:`TestSkipped`. Raised when a resource (such as a network
    connection) is not available. Raised by the :func:`requires` function.
 
-The :mod:`test.test_support` module defines the following constants:
+The :mod:`test.support` module defines the following constants:
 
 
 .. data:: verbose
@@ -278,20 +278,34 @@ The :mod:`test.support` module defines the following functions:
    This will run all tests defined in the named module.
 
 
-.. function:: catch_warning(record=True)
+.. function:: catch_warning(module=warnings, record=True)
 
    Return a context manager that guards the warnings filter from being
-   permanently changed and records the data of the last warning that has been
-   issued. The ``record`` argument specifies whether any raised warnings are
-   captured by the object returned by :func:`warnings.catch_warning` or allowed
-   to propagate as normal.
+   permanently changed and optionally alters the :func:`showwarning`
+   function to record the details of any warnings that are issued in the
+   managed context. Attributes of the most recent warning are saved
+   directly on the context manager, while details of previous warnings
+   can be retrieved from the ``warnings`` list.
 
-   The context manager is typically used like this::
+   The context manager is used like this::
 
       with catch_warning() as w:
+          warnings.simplefilter("always")
           warnings.warn("foo")
           assert str(w.message) == "foo"
-
+          warnings.warn("bar")
+          assert str(w.message) == "bar"
+          assert str(w.warnings[0].message) == "foo"
+          assert str(w.warnings[1].message) == "bar"
+
+   By default, the real :mod:`warnings` module is affected - the ability
+   to select a different module is provided for the benefit of the
+   :mod:`warnings` module's  own unit tests.
+   The ``record`` argument specifies whether or not the :func:`showwarning`
+   function is replaced. Note that recording the warnings in this fashion
+   also prevents them from being written to sys.stderr. If set to ``False``,
+   the standard handling of warning messages is left in place (however, the
+   original handling is still restored at the end of the block).
 
 .. function:: captured_stdout()
 
@@ -331,3 +345,5 @@ The :mod:`test.support` module defines the following classes:
 .. method:: EnvironmentVarGuard.unset(envvar)
 
    Temporarily unset the environment variable ``envvar``.
+
+

Lib/test/support.py

@@ -368,50 +368,67 @@ def open_urlresource(url, *args, **kw):
 
 
 class WarningMessage(object):
-    "Holds the result of the latest showwarning() call"
+    "Holds the result of a single showwarning() call"
+    _WARNING_DETAILS = "message category filename lineno line".split()
+    def __init__(self, message, category, filename, lineno, line=None):
+        for attr in self._WARNING_DETAILS:
+            setattr(self, attr, locals()[attr])
+        self._category_name = category.__name__ if category else None
+
+    def __str__(self):
+        return ("{message : %r, category : %r, filename : %r, lineno : %s, "
+                    "line : %r}" % (self.message, self._category_name,
+                                    self.filename, self.lineno, self.line))
+
+class WarningRecorder(object):
+    "Records the result of any showwarning calls"
     def __init__(self):
-        self.message = None
-        self.category = None
-        self.filename = None
-        self.lineno = None
-
-    def _showwarning(self, message, category, filename, lineno, file=None,
-                        line=None):
-        self.message = message
-        self.category = category
-        self.filename = filename
-        self.lineno = lineno
-        self.line = line
+        self.warnings = []
+        self._set_last(None)
+
+    def _showwarning(self, message, category, filename, lineno,
+                    file=None, line=None):
+        wm = WarningMessage(message, category, filename, lineno, line)
+        self.warnings.append(wm)
+        self._set_last(wm)
+
+    def _set_last(self, last_warning):
+        if last_warning is None:
+            for attr in WarningMessage._WARNING_DETAILS:
+                setattr(self, attr, None)
+        else:
+            for attr in WarningMessage._WARNING_DETAILS:
+                setattr(self, attr, getattr(last_warning, attr))
 
     def reset(self):
-        self._showwarning(*((None,)*6))
+        self.warnings = []
+        self._set_last(None)
 
     def __str__(self):
-        return ("{message : %r, category : %r, filename : %r, lineno : %s, "
-                    "line : %r}" % (self.message,
-                            self.category.__name__ if self.category else None,
-                            self.filename, self.lineno, self.line))
-
+        return '[%s]' % (', '.join(map(str, self.warnings)))
 
 @contextlib.contextmanager
 def catch_warning(module=warnings, record=True):
-    """
-    Guard the warnings filter from being permanently changed and record the
-    data of the last warning that has been issued.
+    """Guard the warnings filter from being permanently changed and
+    optionally record the details of any warnings that are issued.
 
     Use like this:
 
         with catch_warning() as w:
             warnings.warn("foo")
             assert str(w.message) == "foo"
     """
-    original_filters = module.filters[:]
+    original_filters = module.filters
     original_showwarning = module.showwarning
     if record:
-        warning_obj = WarningMessage()
-        module.showwarning = warning_obj._showwarning
+        recorder = WarningRecorder()
+        module.showwarning = recorder._showwarning
+    else:
+        recorder = None
     try:
-        yield warning_obj if record else None
+        # Replace the filters with a copy of the original
+        module.filters = module.filters[:]
+        yield recorder
     finally:
         module.showwarning = original_showwarning
         module.filters = original_filters
@@ -421,7 +438,7 @@ class CleanImport(object):
     """Context manager to force import to return a new module reference.
 
     This is useful for testing module-level behaviours, such as
-    the emission of a DepreciationWarning on import.
+    the emission of a DeprecationWarning on import.
 
     Use like this:
 

Lib/test/test_struct.py

@@ -35,12 +35,9 @@ def with_warning_restore(func):
     @wraps(func)
     def decorator(*args, **kw):
         with catch_warning():
-            # Grrr, we need this function to warn every time.  Without removing
-            # the warningregistry, running test_tarfile then test_struct would fail
-            # on 64-bit platforms.
-            globals = func.__globals__
-            if '__warningregistry__' in globals:
-                del globals['__warningregistry__']
+            # We need this function to warn every time, so stick an
+            # unqualifed 'always' at the head of the filter list
+            warnings.simplefilter("always")
             warnings.filterwarnings("error", category=DeprecationWarning)
             return func(*args, **kw)
     return decorator
@@ -53,7 +50,7 @@ def deprecated_err(func, *args):
         pass
     except DeprecationWarning:
         if not PY_STRUCT_OVERFLOW_MASKING:
-            raise TestFailed("%s%s expected to raise struct.error" % (
+            raise TestFailed("%s%s expected to raise DeprecationWarning" % (
                 func.__name__, args))
     else:
         raise TestFailed("%s%s did not raise error" % (

Lib/test/test_warnings.py

@@ -487,6 +487,47 @@ class CWarningsDisplayTests(BaseTest, WarningsDisplayTests):
 class PyWarningsDisplayTests(BaseTest, WarningsDisplayTests):
     module = py_warnings
 
+class WarningsSupportTests(object):
+    """Test the warning tools from test support module"""
+
+    def test_catch_warning_restore(self):
+        wmod = self.module
+        orig_filters = wmod.filters
+        orig_showwarning = wmod.showwarning
+        with support.catch_warning(wmod):
+            wmod.filters = wmod.showwarning = object()
+        self.assert_(wmod.filters is orig_filters)
+        self.assert_(wmod.showwarning is orig_showwarning)
+        with support.catch_warning(wmod, record=False):
+            wmod.filters = wmod.showwarning = object()
+        self.assert_(wmod.filters is orig_filters)
+        self.assert_(wmod.showwarning is orig_showwarning)
+
+    def test_catch_warning_recording(self):
+        wmod = self.module
+        with support.catch_warning(wmod) 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, [])
+        orig_showwarning = wmod.showwarning
+        with support.catch_warning(wmod, record=False) as w:
+            self.assert_(w is None)
+            self.assert_(wmod.showwarning is orig_showwarning)
+
+
+class CWarningsSupportTests(BaseTest, WarningsSupportTests):
+    module = c_warnings
+
+class PyWarningsSupportTests(BaseTest, WarningsSupportTests):
+    module = py_warnings
+
 
 def test_main():
     py_warnings.onceregistry.clear()
@@ -498,6 +539,7 @@ def test_main():
                                 CWCmdLineTests, PyWCmdLineTests,
                                 _WarningsTests,
                                 CWarningsDisplayTests, PyWarningsDisplayTests,
+                                CWarningsSupportTests, PyWarningsSupportTests,
                              )