Fix nose-devs#777: incorrect descriptions for failed generated tests

The final report was looking at the original function object to
determine the name, but by that time it has been modified and no longer
represents the test that failed.  This caches the description, so the
report summary can get the correct name.

wip: should we just pass in the description directly?  Seems like we
should.

nose/case.py

@@ -197,13 +197,36 @@ def runTest(self):
         self.test(*self.arg)
 
     def shortDescription(self):
+        # We cache the description because of the way we advocate people
+        # set the description for their test.  The set up is typically
+        # something like:
+        #
+        #   def test_generator():
+        #       def func(arg):
+        #           assert ...
+        #       for i in range(10):
+        #           func.description = "test_generator_%d" % i
+        #           yield func, i
+        #
+        # This appears to work early on, but it fails when generating the report
+        # summary at the end of the run.  To prevent it from getting
+        # out-of-sync, we'll go ahead and cache the description the first time
+        # through.
+        if hasattr(self, '_cached_description'):
+            return self._cached_description
+
         if hasattr(self.test, 'description'):
-            return self.test.description
-        func, arg = self._descriptors()
-        doc = getattr(func, '__doc__', None)
-        if not doc:
-            doc = str(self)
-        return doc.strip().split("\n")[0].strip()
+            description = self.test.description
+        else:
+            func, arg = self._descriptors()
+            doc = getattr(func, '__doc__', None)
+            if not doc:
+                doc = str(self)
+            description = doc.strip().split("\n")[0].strip()
+
+        self._cached_description = description
+
+        return description
 
 
 class FunctionTestCase(TestBase):