Eliminate warnings output for tests of deprecated cache methods.

Add a limited mechanism to capture warnings instead of having them
printed to stderr.

Tests work in my local ZODB sandbox.  Need to check whether any Zope 2
or Zope 3 tests call the deprecated methods, which could affect the
test results.

src/ZODB/tests/testConnection.py

@@ -15,10 +15,12 @@
 
 import doctest
 import unittest
+import warnings
 
 from persistent import Persistent
 from ZODB.config import databaseFromString
 from ZODB.utils import p64, u64
+from ZODB.tests.warnhook import WarningsHook
 
 class ConnectionDotAdd(unittest.TestCase):
 
@@ -324,15 +326,63 @@ class UserMethodTests(unittest.TestCase):
         >>> db = databaseFromString("<zodb>\n<mappingstorage/>\n</zodb>")
         >>> cn = db.open()
         >>> r = cn.root()
-        >>> r._p_activate()
-        >>> cn.cacheFullSweep()
-        >>> r._p_state
-        0
         >>> cn.cacheMinimize()
         >>> r._p_state
         -1
-        >>> cn.cacheFullSweep(12)
+
+        The next couple of tests are involved because they have to
+        cater to backwards compatibility issues.  The cacheMinimize()
+        method used to take an argument, but now ignores it.
+        cacheFullSweep() used to do something different than
+        cacheMinimize(), but it doesn't anymore.  We want to verify
+        that these methods do something, but all cause deprecation
+        warnings.  To do that, we need a warnings hook.
+
+        >>> hook = WarningsHook()
+        >>> hook.install()
+
+        >>> r._p_activate()
         >>> cn.cacheMinimize(12)
+        >>> r._p_state
+        -1
+        >>> len(hook.warnings)
+        1
+        >>> message, category, filename, lineno = hook.warnings[0]
+        >>> message
+        'The dt argument to cacheMinimize is ignored.'
+        >>> category.__name__
+        'DeprecationWarning'
+        >>> hook.clear()
+
+        cacheFullSweep() is a doozy.  It generates two deprecation
+        warnings, one from the Connection and one from the
+        cPickleCache.  Maybe we should drop the cPickleCache warning,
+        but it's there for now.  When passed an argument, it acts like
+        cacheGC().  When t isn't passed an argument it acts like
+        cacheMinimize().
+        
+        >>> r._p_activate()
+        >>> cn.cacheFullSweep(12)
+        >>> r._p_state
+        0
+        >>> len(hook.warnings)
+        2
+        >>> message, category, filename, lineno = hook.warnings[0]
+        >>> message
+        'cacheFullSweep is deprecated. Use cacheMinimize instead.'
+        >>> category.__name__
+        'DeprecationWarning'
+        >>> message, category, filename, lineno = hook.warnings[1]
+        >>> message
+        'No argument expected'
+        >>> category.__name__
+        'DeprecationWarning'
+
+        We have to uninstall the hook so that other warnings don't get
+        lost.
+        
+        >>> hook.uninstall()
+    
         """
 
 class InvalidationTests(unittest.TestCase):

src/ZODB/tests/warnhook.py

+##############################################################################
+#
+# Copyright (c) 2004 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+import warnings
+
+class WarningsHook:
+    """Hook to capture warnings generated by Python.
+
+    The function warnings.showwarning() is designed to be hooked by
+    application code, allowing the application to customize the way it
+    handles warnings.
+
+    This hook captures the unformatted warning information and stored
+    it in a list.  A test can inspect this list after the test is over.
+
+    Issues:
+
+    The warnings module has lots of delicate internal state.  If
+    a warning has been reported once, it won't be reported again.  It
+    may be necessary to extend this class with a mechanism for
+    modifying the internal state so that we can be guaranteed a
+    warning will be reported.
+
+    If Python is run with a warnings filter, e.g. python -Werror,
+    then a test that is trying to inspect a particular warning will
+    fail.  Perhaps this class can be extended to install more-specific
+    filters the test to work anyway.
+    """
+
+    def __init__(self):
+        self.original = None
+        self.warnings = []
+
+    def install(self):
+        self.original = warnings.showwarning
+        warnings.showwarning = self.showwarning
+
+    def uninstall(self):
+        assert self.original is not None
+        warnings.showwarning = self.original
+        self.original = None
+
+    def showwarning(self, message, category, filename, lineno):
+        self.warnings.append((str(message), category, filename, lineno))
+
+    def clear(self):
+        self.warnings = []
+