Index: unittest.py
===================================================================
--- unittest.py	(revision 60224)
+++ unittest.py	(working copy)
@@ -412,10 +412,11 @@
 
     def addTest(self, test):
         # sanity checks
+        import unittest
         if not callable(test):
             raise TypeError("the test to add must be callable")
         if (isinstance(test, (type, types.ClassType)) and
-            issubclass(test, (TestCase, TestSuite))):
+            issubclass(test, (unittest.TestCase, unittest.TestSuite))):
             raise TypeError("TestCases and TestSuites must be instantiated "
                             "before passing them to addTest()")
         self._tests.append(test)
@@ -499,7 +500,8 @@
 
     def loadTestsFromTestCase(self, testCaseClass):
         """Return a suite of all tests cases contained in testCaseClass"""
-        if issubclass(testCaseClass, TestSuite):
+        import unittest
+        if issubclass(testCaseClass, unittest.TestSuite):
             raise TypeError("Test cases should not be derived from TestSuite. Maybe you meant to derive from TestCase?")
         testCaseNames = self.getTestCaseNames(testCaseClass)
         if not testCaseNames and hasattr(testCaseClass, 'runTest'):
@@ -508,11 +510,12 @@
 
     def loadTestsFromModule(self, module):
         """Return a suite of all tests cases contained in the given module"""
+        import unittest
         tests = []
         for name in dir(module):
             obj = getattr(module, name)
             if (isinstance(obj, (type, types.ClassType)) and
-                issubclass(obj, TestCase)):
+                issubclass(obj, unittest.TestCase)):
                 tests.append(self.loadTestsFromTestCase(obj))
         return self.suiteClass(tests)
 
@@ -525,6 +528,7 @@
 
         The method optionally resolves the names relative to a given module.
         """
+        import unittest
         parts = name.split('.')
         if module is None:
             parts_copy = parts[:]
@@ -543,7 +547,7 @@
         if type(obj) == types.ModuleType:
             return self.loadTestsFromModule(obj)
         elif (isinstance(obj, (type, types.ClassType)) and
-              issubclass(obj, TestCase)):
+              issubclass(obj, unittest.TestCase)):
             return self.loadTestsFromTestCase(obj)
         elif type(obj) == types.UnboundMethodType:
             return parent(obj.__name__)