How to get Mock().assert_called_once like behavior below python 3.6?

Question

How to get unittest.mock.Mock().assert_called_once like behavior with unittest.mock.Mock().assert_called_once_with , as assert_called_once s not available below python 3.6 .

Basically what I want is checking if the method gets called exactly once, no matter with which argument or how many argument.

I tried unittest.mock.ANY , but seems it isn't what I want.

Answer 1

All that assert_called_once() does is assert that the Mock.call_count attribute is 1; you can trivially do the same test:

self.assertEqual(
    mock_object.call_count, 1,
    "Expected mock to have been called once. Called {} times.".format(
        mock_object.call_count))

If you tried to use Mock.assert_called_once_with() with the ANY object, take into account that that object stands for the value of one of the arguments . Mock.assert_called_once_with(ANY) only matches if the object has been called with exactly one argument , and the value of that argument doesn't matter:

>>> from unittest.mock import Mock, ANY
>>> m = Mock()
>>> m(42, 81, spam='eggs')  # 2 positional arguments, one keyword argument
<Mock name='mock()' id='4348527952'>
>>> m.assert_called_once_with(ANY)   # doesn't match, just one positional argument
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/mock.py", line 825, in assert_called_once_with
    return self.assert_called_with(*args, **kwargs)
  File "/Users/mjpieters/Development/Library/buildout.python/parts/opt/lib/python3.6/unittest/mock.py", line 814, in assert_called_with
    raise AssertionError(_error_message()) from cause
AssertionError: Expected call: mock(<ANY>)
Actual call: mock(42, 81, spam='eggs')

You can't use the ANY object together with the *called_with assertions to mean 'any number of arguments'. Only in an assertion that takes call() objects would ANY be interpreted as any number of arguments ; so you could also use Mock.assert_has_calls() here, passing in a list with a single ANY element:

>>> m.assert_has_calls([ANY])  # no exception raised