Could not load depended fixtures for chaining dependencies

[coderfly]

class FixtureInnerLevel2(Fixture):
    document_class = Simple

    data_file = 'tests.data.fixture_simple'


class FixtureInnerLevel1(Fixture):
    document_class = Simple

    depends = {
        'level2': FixtureInnerLevel2
    }

    data_file = 'tests.data.fixture_simple'


class FixtureInnerMain(Fixture):
    document_class = Simple

    depends = {
        'level1': FixtureInnerLevel1
    }

    data_file = 'tests.data.fixture_simple'