Fix tests so they pass in -R mode

Lib/test/test_decimal.py

@@ -42,6 +42,8 @@ Signals = getcontext().flags.keys()
 
 # Tests are built around these assumed context defaults.
 # test_main() restores the original context.
+def init():
+    global ORIGINAL_CONTEXT
     ORIGINAL_CONTEXT = getcontext().copy()
     DefaultContext.prec = 9
     DefaultContext.rounding = ROUND_HALF_EVEN
@@ -1069,6 +1071,7 @@ def test_main(arith=False, verbose=None):
     is enabled in regrtest.py
     """
 
+    init()
     global TEST_ALL
     TEST_ALL = arith or is_resource_enabled('decimal')
 

Lib/test/test_difflib.py

@@ -152,6 +152,10 @@ class TestSFpatches(unittest.TestCase):
         difflib.SequenceMatcher(None, old, new).get_opcodes()
 
 
+def test_main():
+    difflib.HtmlDiff._default_prefix = 0
     Doctests = doctest.DocTestSuite(difflib)
-
     run_unittest(TestSFpatches, TestSFbugs, Doctests)
+
+if __name__ == '__main__':
+    test_main()

Lib/test/test_warnings.py

@@ -84,5 +84,9 @@ class TestModule(unittest.TestCase):
 def test_main(verbose=None):
     test_support.run_unittest(TestModule)
 
+# Obscure hack so that this test passes after reloads (regrtest -R).
+if '__warningregistry__' in globals():
+    del globals()['__warningregistry__']
+
 if __name__ == "__main__":
     test_main(verbose=True)