$ python fizzbuzz_test.py 
..F.
======================================================================
FAIL: test_FizzBuzz (__main__.TestFizzBuzz)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "fizzbuzz_test.py", line 22, in test_FizzBuzz
    self.assertEqual(FizzBuzz(15), "fizzbuzz")
AssertionError: 'fizz' != 'fizzbuzz'

----------------------------------------------------------------------
Ran 4 tests in 0.000s

FAILED (failures=1)