CODEWITHSUNDEEP
pythonunit-testingmocking
CppLearner
CppLearner

Reputation: 17040

Mocking - How do I raise exception on the caller?

Suppose this is the code

def move(*args, **kwargs):   
    try:
        shutil.move(source, destination)
    except Exception as e:
        raise e

and in my tests.py

@patch.object(shutil, 'move')
def test_move_catch_exception(self, mock_rmtree):
    ''' Tests moving a target hits exception. '''
    mock_rmtree.side_effect = Exception('abc')
    self.assertRaises(Exception, move,
                             self.src_f, self.src_f, **self.kwargs)

It said this

  File "unittests.py", line 84, in test_move_catch_exception
    self.src_f, self.src_f, **self.kwargs)
AssertionError: Exception not raised

If I assert on mock_rmtree it will pass. How can I assert on the caller (in this case, the function move)?

As aquavitae pointed out, the primary reasons was copy-paste error, and also I was asserting a tuple in the beginning. Always asseert with the right return type...

Upvotes: 19

Views: 24472

Answers (1)

aquavitae
aquavitae

Reputation: 19114

You've got a typo in your example, missing a '.

Its not entirely clear what you're asking, but if I understand you correctly, you're asking how to test that a raised exception is caught inside move. One problem is that you're patching shutil.rmtree, not shutil.move, but you can't be certain thatshutil.rmtree will ever be called. shutil.move only actually calls shutil.rmtree if it successfully copies a directory, but since you're copying self.src_f to itself, this doesn't happen. This is not a very good way of patching it though, because the assumption that shutil.move will call shutil.rmtree at all is not guaranteed and is implementation dependent.

As for how to test it, simply check that the return value is as expected:

@patch.object(shutil, 'move')
def test_move_catch_exception(self, mock_move):
    ''' Tests moving a target hits exception. '''
    e = OSError('abc')
    mock_move.side_effect = e
    returns = move(self.src_f, self.src_f, **self.kwargs)
    assert returns == (False, e)

Upvotes: 27

Related Questions