output

F
======================================================================
FAIL: test_foo (__main__.FooTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/l/.IntelliJIdea2017.3/config/scratches/scratch.py", line 11, in test_foo
    self.assertEqual(expected, actual)
AssertionError: 'foobar' != <MagicMock name='mock.foo()' id='140619506578448'>

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (failures=1)

test_foo.py

from mock import MagicMock
from unittest import TestCase, main


class FooTest(TestCase):
    def test_foo(self):
        expected = 'foobar'
        bar = MagicMock()
        bar.func.return_value = expected
        actual = bar.foo()
        self.assertEqual(expected, actual)

def foo(bar):
    return bar.func()

main()