tests: Reuse unittest's functions & classes when present.

Fixes unittest.expectedFailure usage, allowing phasing out
backportUnittest gradually (at least for the backport part).

product/ERP5Type/tests/backportUnittest.py

@@ -9,7 +9,16 @@ import unittest
 import sys
 import time
 
-class SkipTest(Exception):
+try:
+    SkipTest = unittest.SkipTest
+    _ExpectedFailure = unittest.case._ExpectedFailure
+    _UnexpectedSuccess = unittest.case._UnexpectedSuccess
+    skip = unittest.skip
+    skipIf = unittest.skipIf
+    skipUnless = unittest.skipUnless
+    expectedFailure = unittest.expectedFailure
+except AttributeError:
+    class SkipTest(Exception):
         """
         Raise this exception in a test to skip it.
 
@@ -18,7 +27,7 @@ class SkipTest(Exception):
         """
         pass
 
-class _ExpectedFailure(Exception):
+    class _ExpectedFailure(Exception):
         """
         Raise this when a test is expected to fail.
 
@@ -29,25 +38,16 @@ class _ExpectedFailure(Exception):
             Exception.__init__(self)
             self.exc_info = exc_info
 
-class _UnexpectedSuccess(Exception):
+    class _UnexpectedSuccess(Exception):
       """
       The test was supposed to fail, but it didn't!
       """
       pass
 
-class SetupSiteError(Exception):
-    """
-    The ERP5 Site could not have been setup.
-    This is raised when the site could not have been created in a previous
-    test. We want this to count as an error, but we do not want this to happear
-    in traceback for readability.
-    """
-    pass
-
-def _id(obj):
+    def _id(obj):
         return obj
 
-def skip(reason):
+    def skip(reason):
         """
         Unconditionally skip a test.
         """
@@ -63,7 +63,7 @@ def skip(reason):
             return skip_wrapper
         return decorator
 
-def skipIf(condition, reason):
+    def skipIf(condition, reason):
         """
         Skip a test if the condition is true.
         """
@@ -71,7 +71,7 @@ def skipIf(condition, reason):
             return skip(reason)
         return _id
 
-def skipUnless(condition, reason):
+    def skipUnless(condition, reason):
         """
         Skip a test unless the condition is true.
         """
@@ -80,7 +80,7 @@ def skipUnless(condition, reason):
         return _id
 
 
-def expectedFailure(func):
+    def expectedFailure(func):
         def wrapper(*args, **kwargs):
             try:
                 func(*args, **kwargs)
@@ -91,6 +91,15 @@ def expectedFailure(func):
         wrapper.__doc__ = func.__doc__
         return wrapper
 
+class SetupSiteError(Exception):
+    """
+    The ERP5 Site could not have been setup.
+    This is raised when the site could not have been created in a previous
+    test. We want this to count as an error, but we do not want this to happear
+    in traceback for readability.
+    """
+    pass
+
 class TestCase(unittest.TestCase):
     """We redefine here the run() method, and add a skipTest() method.
     """