Google App Engine Unittest: Difficulty with AssertEquals

Question

I have a unit test for my GAE app:

def test_getNeighborhoodKeys_twoCourses(self):
            cs1110, cs2110 = testutils.setUpSimpleCourses()

            foo = getFooResult()
            bar = getBarResult()

    self.assertEquals(foo, bar) # fails

This is the failure:

AssertionError: set([CS 1110: Untitled, CS 2110: Untitled]) != set([CS 2110: Untitled, CS 1110: Untitled])

It looks to me like the test should pass. What's going wrong?

Answer 1

Looks like the items belonging to sets foo and bar are of some extremely funky type which overrides __repr__ -- otherwise, with normal types, there would be quotes to clarify exactly what's inside those brackets. Thus, that type must also override __eq__ to determine equality conditions (otherwise, by default, two instances are equal only if they're the same instance). You could alternatively override __cmp__, but that's a pretty old and dusty approach -- specific comparisons such as __eq__ are vastly preferred nowadays!

If you do override __eq__ (or __cmp__ for that matter) be sure to also override __hash__ because it's crucial that two instances that compare equal have exactly the same hash too, otherwise use of such instances as members of sets, or keys in dictionaries, misbehaves in very hard to predict ways.