Mocking File Objects Or Iterables In Python

Which way is proper for mocking and testing code that iters object returned by open(), using mock library? whitelist_data.py: WHITELIST_FILE = 'testdata.txt' format_str = lambda s

Solution 1:

You're looking for a MagicMock. This supports iteration.

In mock 0.80beta4, patch returns a MagicMock. So this simple example works:

import mock

deffoo():
    for line inopen('myfile'):
        print line

@mock.patch('__builtin__.open')deftest_foo(open_mock):
    foo()
    assert open_mock.called

If you're running mock 0.7.x (It looks like you are), I don't think you can accomplish this with patch alone. You'll need to create the mock separately, then pass it into patch:

import mock

deffoo():
    for line inopen('myfile'):
        print line

deftest_foo():
    open_mock = mock.MagicMock()
    with mock.patch('__builtin__.open', open_mock):
        foo()
        assert open_mock.called

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Note - I've run these with py.test, however, these same approaches will work with unittest as well.