pytest-bdd/pytest_bdd/steps.py

"""Step decorators.

Example:

@given('I have an article')
def article(author):
    return create_test_article(author=author)


@when('I go to the article page')
def go_to_the_article_page(browser, article):
    browser.visit(urljoin(browser.url, '/articles/{0}/'.format(article.id)))


@then('I should not see the error message')
def no_error_message(browser):
    with pytest.raises(ElementDoesNotExist):
        browser.find_by_css('.message.error').first


Multiple names for the steps:

@given('I have an article')
@given('there is an article')
def article(author):
    return create_test_article(author=author)


Reusing existing fixtures for a different step name:

given('I have a beautiful article', fixture='article')

"""
import inspect
import sys

import pytest

from pytest_bdd.feature import remove_prefix
from pytest_bdd.types import GIVEN, WHEN, THEN


class StepError(Exception):
    pass


def given(name, fixture=None):
    """Given step decorator.

    :param name: Given step name.
    :param fixture: Optional name of the fixture to reuse.

    :raises: StepError in case of wrong configuration.
    :note: Can't be used as a decorator when the fixture is specified.
    """
    name = remove_prefix(name)
    if fixture is not None:
        module = get_caller_module()
        func = lambda: lambda request: request.getfuncargvalue(fixture)
        setattr(module, name, pytest.fixture(func))
        return _not_a_fixture_decorator

    return _step_decorator(GIVEN, name)


def when(name):
    """When step decorator.

    :param name: Step name.
    :raises: StepError in case of wrong configuration.
    """
    return _step_decorator(WHEN, name)


def then(name):
    """Then step decorator.

    :param name: Step name.
    :raises: StepError in case of wrong configuration.
    """
    return _step_decorator(THEN, name)


def _not_a_fixture_decorator(func):
    """Function that prevents the decoration.

    :param func: Function that is going to be decorated.
    :raises: `StepError` if was used as a decorator.
    """
    raise StepError('Cannot be used as a decorator when the fixture is specified')


def _step_decorator(step_type, step_name):
    """Step decorator for the type and the name.
    :param step_type: Step type (GIVEN, WHEN or THEN).
    :param step_name: Step name as in the feature file.

    :return: Decorator function for the step.

    :note: If the step type is GIVEN it will automatically apply the pytest
    fixture decorator to the step function.
    """
    step_name = remove_prefix(step_name)

    def decorator(func):
        step_func = func
        if step_type == GIVEN:
            if not hasattr(func, '_pytestfixturefunction'):
                # avoid overfixturing of a fixture
                func = pytest.fixture(func)
            step_func = lambda request: request.getfuncargvalue(func.func_name)

        step_func.__name__ = step_name
        setattr(get_caller_module(), step_name, pytest.fixture(lambda: step_func))
        return func

    return decorator


def get_caller_module(depth=2):
    """Return the module of the caller."""
    frame = sys._getframe(depth)
    return inspect.getmodule(frame)