python.md

Python tricks

Substituting a method (function) by a mock in a test

There are many ways, but find here two that I found useful.

• Using the @patch.object decorator.

ClassToPatch.method_to_patch is the method to patch. mock_method is the method used to patch it. autospec is important to have a mocking method with the same attributes (and methods, it we were patching a class) than the patched object. In the test, mock is the mock (created by the decorator, based on mock_method and the spec of the method to patch):

fromunittest.mockimportpatchdefmock_method(arg1, arg2...):
...
@patch.object(ClassToPatch, 'method_to_patch', side_effect=mock_method,autospec=True)deftest_something(self, mock):
...
# Check that the mock was called count timesself.assertEqual(mock.call_count, count)

• Using a patch.object context.

Same as above, but instead of the decorator on the testing function, I use a patch context:

 def test_something(self):
with patch.object(ClassToPatch, 'method_to_patch',
side_effect=mock_method, autospec=True) as mock:
...
# Check that the mock was called count times
self.assertEqual(mock.call_count, count)