#16835: update PEP 399 idiom to make it compatible with unittest test discovery.

pep-0399.txt

@@ -8,7 +8,7 @@ Type: Informational
 Content-Type: text/x-rst
 Created: 04-Apr-2011
 Python-Version: 3.3
-Post-History: 04-Apr-2011, 12-Apr-2011, 17-Jul-2011, 15-Aug-2011
+Post-History: 04-Apr-2011, 12-Apr-2011, 17-Jul-2011, 15-Aug-2011, 01-Jan-2013
 
 Abstract
 ========
@@ -124,7 +124,7 @@ C accelerated versions of a module, a basic idiom can be followed::
     py_heapq = import_fresh_module('heapq', blocked=['_heapq'])
 
 
-    class ExampleTest(unittest.TestCase):
+    class ExampleTest:
 
         def test_heappop_exc_for_non_MutableSequence(self):
             # Raise TypeError when heap is not a
@@ -136,34 +136,35 @@ C accelerated versions of a module, a basic idiom can be followed::
                     return 0
 
             heap = Spam()
-            self.assertFalse(isinstance(heap,
-                                collections.abc.MutableSequence))
+            self.assertIsInstance(heap, collections.abc.MutableSequence)
             with self.assertRaises(TypeError):
                 self.heapq.heappop(heap)
 
 
-    class AcceleratedExampleTest(ExampleTest):
-
-        """Test using the accelerated code."""
-
-        heapq = c_heapq
-
-
-    class PyExampleTest(ExampleTest):
-
+    class PyExampleTest(ExampleTest, unittest.TestCase):
         """Test with just the pure Python code."""
-
         heapq = py_heapq
 
 
-    def test_main():
-        run_unittest(AcceleratedExampleTest, PyExampleTest)
+    @unittest.skipUnless(c_heapq, 'requires the C _heapq module')
+    class CExampleTest(ExampleTest, unittest.TestCase):
+        """Test using the accelerated code."""
+        heapq = c_heapq
 
 
     if __name__ == '__main__':
-        test_main()
+        unittest.main()
 
 
+The test module defines a base class (``ExampleTest``) with test methods
+that access the ``heapq`` module through a ``self.heapq`` class attribute,
+and two subclasses that set this attribute to either the Python or the C
+version of the module.  Note that only the two subclasses inherit from
+``unittest.TestCase`` -- this prevents the ``ExampleTest`` class from
+being detected as a ``TestCase`` subclass by ``unittest`` test discovery.
+A ``skipUnless`` decorator can be added to the class that tests the C code
+in order to have these tests skipped when the C module is not available.
+
 If this test were to provide extensive coverage for
 ``heapq.heappop()`` in the pure Python implementation then the
 accelerated C code would be allowed to be added to CPython's standard