def METHOD_NAME(open_mock, subprocess_mock, getmtime_mock):
    getmtime_mock.side_effect = [
        # The first call is for the source
        1531144805.1225898,
        # The second call is for the destination
        1530885814.6340182,
    ]
    from_string('{{ css("compiled", debug=True) }}")').render()
    source = os.path.realpath(
        os.path.join(settings.ROOT, 'static/css/impala/buttons.less')
    )
    assert subprocess_mock.Popen.mock_calls == [
        mock.call([settings.LESS_BIN, source], stdout=mock.ANY)
    ]