warnings.resetwarnings() should never be called by tests.

Doing so wipes out all the warning filters other tests may set
up to suppress warnings those tests need to provoke but want to
hide from the entity running the tests.

This stops all the DeprecationWarnings that were displayed from
the ZODB and ZEO tests when running Zope trunk's test suite.

lib/python/AccessControl/tests/testDeprecatedAPI.py

@@ -25,10 +25,17 @@ import unittest, warnings
 
 class DeprecatedAPI(unittest.TestCase):
     def setUp(self):
+        # There is no official API to restore warning filters to a previous
+        # state.  Here we cheat.
+        self.original_warning_filters = warnings.filters[:]
+
         # We test for warnings by turning them into exceptions
         warnings.filterwarnings('error', category=DeprecationWarning,
             module='AccessControl')
 
+    def tearDown(self):
+        warnings.filters[:] = self.original_warning_filters
+
     def testDeprecatedHasRole(self):
         # hasRole has been deprecated, we expect a warning.
         try:
@@ -48,11 +55,6 @@ class DeprecatedAPI(unittest.TestCase):
         else:
             pass
 
-    def tearDown(self):
-        warnings.resetwarnings()
-        warnings.simplefilter("ignore", category=PendingDeprecationWarning)
-        warnings.simplefilter("ignore", category=OverflowWarning)
-
 class BasicUser(DeprecatedAPI):
     userObject = User.SimpleUser('JoeBloke', '123', [], [])
 

lib/python/Zope2/Startup/tests/test_warnfilter.py

@@ -46,11 +46,12 @@ class TestWarnFilter(unittest.TestCase):
     def setUp(self):
         if self.schema is None:
             TestWarnFilter.schema = getSchema()
+        # There is no official API to restore warning filters to a previous
+        # state.  Here we cheat.
+        self.original_warning_filters = warnings.filters[:]
 
     def tearDown(self):
-        warnings.resetwarnings()
-        warnings.simplefilter("ignore", category=PendingDeprecationWarning)
-        warnings.simplefilter("ignore", category=OverflowWarning)
+        warnings.filters[:] = self.original_warning_filters
 
     def load_config_text(self, text):
         # We have to create a directory of our own since the existence