generic lettuce steps for Django models

After I left the Bureau approximately a month ago I’ve taken up a new role with Infoxchange Australia. My first project here is working on a rewrite of an application using Django.

People here are really into behaviour driven testing, and we’re using Lettuce to do it (using a branch with better Django integration).

I sort of dislike this sort of testing, because it creates an annoying abstraction layer on top of the code, with a poorly defined, quasi-real language. It’s like a bad knock off of Applescript. Anyway, I got sick of defining steps per model, so I put together some generic steps for manipulating Django models (that I’ll have to contribute back).

Anyway they look like this (examples of the step in the docstrings):

# build a hash of model verbose names to models
# this is used by get_model()
def _models_generator():
    for model in get_models():
        yield (model._meta.verbose_name, model)
        yield (model._meta.verbose_name_plural, model)

MODELS = dict(_models_generator())


def get_model(model):
    """
    Convert a model's verbose name to the model class. This allows us to
    use the models verbose name in steps.
    """

    name = model.lower()
    model = MODELS.get(model, None)

    assert model, "Could not locate model by name '%s'" % name

    return model


def create_models(model, hashes):
    for hash_ in hashes:
        model.objects.create(**hash_)


def models_exist(model, hashes):
    for hash_ in hashes:
        assert \
            model.objects.filter(**hash_).exists(), \
            "Object does not exist"


@step(r'I have ([a-z][a-z0-9_ ]*) in the database:')
def create_models_generic(step, model):
    """
    And I have admin field values in the database:
    | name         | value   |
    | project_type | Twine   |

    The generic method can be overridden for a specific model by defining a
    function create_badgers(step), which creates the Badger model.
    """

    try:
        globals()['create_%s' % model](step)
    except KeyError:
        model = get_model(model)

        create_models(model, step.hashes)


@step(r'(?:Given|And|Then) ([A-Z][a-z0-9_ ]*) with ([a-z]+) "([^"]*)" has ([A-Z][a-z0-9_ ]*) in the database:')  # noqa
def create_models_for_relation(step, rel_model_name,
                               rel_key, rel_value, model):
    """
    And project with name "Ball Project" has goals in the database:
    | description                             |
    | To have fun playing with balls of twine |
    """

    lookup = {rel_key: rel_value}
    rel_model = get_model(rel_model_name).objects.get(**lookup)

    for hash_ in step.hashes:
        hash_['%s_id' % rel_model_name] = rel_model.id

    create_models_generic(step, model)


@step('(?:Given|And|Then) ([A-Z][a-z0-9_ ]*) should be present in the database')
def step_models_exist(step, model):
    """
    And objectives should be present in the database:
    | description      |
    | Make a mess      |
    """

    model = get_model(model)

    models_exist(model, step.hashes)


@step(r'There should be (\d+) ([a-z][a-z0-9_ ]*) in the database')
def model_count(step, count, model):
    """
    Then there should be 0 goals in the database
    """

    model = get_model(model)

    assert_equals(model.objects.count(), int(count))

About Danielle

Danielle is an Australian software engineer, computer scientist and feminist. She has worked on GNOME for some time now. Opinions and writing are solely her own and so not represent her employer, the GNOME Foundation, or anyone else but herself.
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