Assertions not rewritten for steps in files with names that don't match Pytest's python_files setting

pytest-bdd steps in files with names that don't match pytest's patterns in thepython_files settings, like steps.py, given.py, when.py then.py, are not picked up by pytests assertion rewriting.

Here's a simple setup to reproduce: https://github.com/blaise-io/pytest-bdd-assertion-rewrite-issue.

In most apps this can be fixed by using pytest.register_assert_rewrite to register modules containing steps, but I'd expect pytest-bdd to either do that for me or for pytest-bdd to warn me about this limitation.

For pytest-bdd to register steps modules magically seemed only possible with heavy monkey patching, as pytest does not allow registering a module for rewriting when the module is already imported. The following code registers the module of a steps for assertion rewriting, which is to demonstrate why monkey patching is a bad idea:

    # append to pytest_bdd.steps.contribute_to_module
    from _pytest.assertion import rewrite
    from six.moves import reload_module
    for hook in sys.meta_path:
        if isinstance(hook, rewrite.AssertionRewritingHook):
            # Add module file name to python_files patterns
            if module.__file__ not in hook.fnpats:
                hook.fnpats.append(module.__file__)
            # Remove module path from checks
            if name in hook._rewritten_names:
                hook._rewritten_names.remove(name)
            # Force-reload the module after our rewrite in setattr
            reload_module(module)
            break

Use the linked reproduction project first, then inspect pytest_bdd.steps.contribute_to_module and pytest.register_assert_rewrite. Determine how step modules are imported relative to pytest's assertion-rewriting patterns; done means steps in files such as steps.py receive assertion rewriting, or the limitation is clearly reported to users.