Use inspect.getdoc rather than assuming __doc__

This means that the tests are testing what a user will
actually see.

tests/test_inheritDoc.py

@@ -94,10 +94,11 @@ class InheritDocTestCase(unittest.TestCase):
     def test_no_inheritdoc(self):
         self.assertIsNone(NoInheritDoc.method2.__doc__)
         self.assertEqual(inspect.getdoc(NoInheritDoc.method2), "Return Method 2.")
+        self.assertIsNone(inspect.getdoc(NoInheritDoc.method5))
 
     def test_inheritDoc(self):
         self.assertEqual(
-            InheritDoc.method1.__doc__,
+            inspect.getdoc(InheritDoc.method1),
             """Return Method 1.
 
 A note.
@@ -107,14 +108,14 @@ def test_inheritDoc(self):
 New line.""",
         )
         self.assertEqual(
-            InheritDoc.method2.__doc__,
+            inspect.getdoc(InheritDoc.method2),
             """Return Method 2.
 
 Note on method 2.""",
         )
-        self.assertEqual(InheritDoc.method3.__doc__, "Note on method 3.")
-        self.assertEqual(InheritDoc.method4.__doc__, "Return Method 4.")
-        self.assertIsNone(InheritDoc.method5.__doc__)
+        self.assertEqual(inspect.getdoc(InheritDoc.method3), "Note on method 3.")
+        self.assertEqual(inspect.getdoc(InheritDoc.method4), "Return Method 4.")
+        self.assertIsNone(inspect.getdoc(InheritDoc.method5))
 
 
 if __name__ == "__main__":