compare generator objects within mock.assert_has_calls

Question

I'm writing a unit test for a function that will confirm that a function called within it is called with the correct arguments. The problem is that one of the arguments is a generator.

Is there a way to compare the contents of the generator that fn is called with using assert_has_calls ? An example of the behavior that I'm looking for is exhibited in 'AssertSequenceEqual.' As it is, test_use_fn fails because the generator objects that it is comparing are different.

import mock

def fn(entries):
    pass

def use_fn(entries, convert=lambda x: x):
    entries = (convert(entry) for entry in entries)
    entries = fn(entries)
    entries = fn(entries)

@mock.patch('fn')
def test_use_fn(self, mock_fn):
    mock_fn.return_value = 'baz'
    entries = ['foo', 'bar']
    use_fn(entries)
    call_1 = mock.call((entry for entry in entries))
    call_2 = mock.call('baz')
    mock_fn.assert_has_calls([call_1, call_2])

Answer 1

You can use call_args_list https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock.call_args_list

I assume that you would check if every items of the generators are the same. I write a assertEqualGenerators() method of the test case class that do the work (if the arguments are not generators use standard assertEqual() ). The module file name is mock_generators.py and you must use mock_generators.fn to patch fn . The last trick is the call object arguments: take a look to https://docs.python.org/3/library/unittest.mock.html#unittest.mock.call.call_list for the dettails of how fetch the data (in your case the first element is what you need).

import unittest
from unittest import mock

def fn(entries):
    pass

def use_fn(entries, convert=lambda x: x):
    entries = (convert(entry) for entry in entries)
    entries = fn(entries)
    entries = fn(entries)

class MyTestCase(unittest.TestCase):

    def assertEqualGenerators(self,a,b):
        try:
            for x,y in zip(a,b):
                self.assertEqual(x, y)
        except TypeError:
            self.assertEqual(a, b)

    @mock.patch("mock_generators.fn")
    def test_use_fn(self, mock_fn):
        mock_fn.return_value = 'baz'
        entries = ['foo', 'bar']
        use_fn(entries)
        calls = [mock.call((entry for entry in entries)),
                    mock.call('baz')]
        self.assertEqual(len(calls), mock_fn.call_count)
        for a,b in zip(mock_fn.call_args_list,calls):
            self.assertEqualGenerators(a[0],b[0])


if __name__ == '__main__':
    unittest.main()