Python: self.assertEqual(a, b, msg) --> I want diff AND msg

Question

If I call it like this, I see a nice diff:

self.assertEqual(a, b)

If I call it like this, I see the msg only:

self.assertEqual(a, b, msg)

Is there an easy way to show the diff AND the msg?

Implementing assertEqual() myself would work, but I ask myself if this is really the best way.

Plattform: Python2.7 and pytest 2.6.2.

Answer 1

If you set longMessage attribute True, you will see both message.

Example:

class TestFoo(unittest.TestCase):

    longMessage = True  # <--

    def test_foo(self):
        self.assertEqual(1+2, 2, 'custom message')

output:

F
======================================================================
FAIL: test_foo (__main__.TestFoo)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "t.py", line 6, in test_foo
    self.assertEqual(1+2, 2, 'custom message')
AssertionError: 3 != 2 : custom message

----------------------------------------------------------------------
Ran 1 test in 0.000s

Answer 2

Since you're using pytest, you could also use pytest's plain assertions instead of the unittest compatibility:

def test_foo():
    assert "abcdefg" == "abcde", "My message"

Output:

====================== FAILURES ======================
______________________ test_foo ______________________

    def test_foo():
>       assert "abcdefg" == "abcde", "My message"
E       AssertionError: My message
E       assert 'abcdefg' == 'abcde'
E         - abcdefg
E         ?      --
E         + abcde