pytest-bdd 0.5.2

BDD for pytest

BDD library for the py.test runner

pytest-bdd implements a subset of Gherkin language for the automation of the project requirements testing and easier behavioral driven development.

Unlike many other BDD tools it doesn’t require a separate runner and benefits from the power and flexibility of the pytest. It allows to unify your unit and functional tests, easier continuous integration server configuration and maximal reuse of the tests setup.

Pytest fixtures written for the unit tests can be reused for the setup and actions mentioned in the feature steps with dependency injection, which allows a true BDD just-enough specification of the requirements without maintaining any context object containing the side effects of the Gherkin imperative declarations.

Install pytest-bdd

pip install pytest-bdd

Example

publish_article.feature:

Scenario: Publishing the article
    Given I'm an author user
    And I have an article
    When I go to the article page
    And I press the publish button
    Then I should not see the error message
    And the article should be published  # Note: will query the database

test_publish_article.py:

from pytest_bdd import scenario, given, when, then

test_publish = scenario('publish_article.feature', 'Publishing the article')


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


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


@when('I press the publish button')
def publish_article(browser):
    browser.find_by_css('button[name=publish]').first.click()


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


@then('And the article should be published')
def article_is_published(article):
    article.refresh()  # Refresh the object in the SQLAlchemy session
    assert article.is_published

Step aliases

Sometimes it is needed to declare the same fixtures or steps with the different names for better readability. In order to use the same step function with multiple step names simply decorate it multiple times:

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

Note that the given step aliases are independent and will be executed when mentioned.

For example if you associate your resource to some owner or not. Admin user can’t be an author of the article, but articles should have a default author.

Scenario: I'm the author
    Given I'm an author
    And I have an article


Scenario: I'm the admin
    Given I'm the admin
    And there is an article

Step parameters

Scenarios can be parametrized to cover few cases. In Gherkin the variable templates are written using corner braces as <somevalue>.

Example:

Scenario: Parametrized given, when, thens
    Given there are <start> cucumbers
    When I eat <eat> cucumbers
    Then I should have <left> cucumbers

Unlike other tools, pytest-bdd implements the scenario outline not in the feature files, but in the python code using pytest parametrization. The reason for this is that it is very often that some simple pythonic type is needed in the parameters like a datetime or a dictionary, which makes it more difficult to express in the text files and preserve the correct format.

The code will look like:

# Here we use pytest to parametrize the test with the parameters table
@pytest.mark.parametrize(
    ['start', 'eat', 'left'],
    [(12, 5, 7)])
@scenario(
    'parametrized.feature',
    'Parametrized given, when, thens',
)
# Note that we should take the same arguments in the test function that we use
# for the test parametrization either directly or indirectly (fixtures depend on them).
def test_parametrized(start, eat, left):
    """We don't need to do anything here, everything will be managed by the scenario decorator."""


@given('there are <start> cucumbers')
def start_cucumbers(start):
    return dict(start=start)


@when('I eat <eat> cucumbers')
def eat_cucumbers(start_cucumbers, start, eat):
    start_cucumbers['eat'] = eat


@then('I should have <left> cucumbers')
def should_have_left_cucumbers(start_cucumbers, start, eat, left):
    assert start - eat == left
    assert start_cucumbers['start'] == start
    assert start_cucumbers['eat'] == eat

Reuse fixtures

Sometimes scenarios define new names for the fixture that can be inherited. Fixtures can be reused with other names using given():

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

Reuse steps

It is possible to define some common steps in the parent conftest.py and simply expect them in the child test file.

common_steps.feature:

Scenario: All steps are declared in the conftest
    Given I have a bar
    Then bar should have value "bar"

conftest.py:

from pytest_bdd import given, then


@given('I have a bar')
def bar():
    return 'bar'


@then('bar should have value "bar"')
def bar_is_bar(bar):
    assert bar == 'bar'

test_common.py:

test_conftest = scenario('common_steps.feature', 'All steps are declared in the conftest')

There are no definitions of the steps in the test file. They were collected from the parent conftests.

Feature file paths

But default, pytest-bdd will use current module’s path as base path for finding feature files, but this behaviour can be changed by having fixture named ‘pytestbdd_feature_base_dir’ which should return the new base path.

test_publish_article.py:

import pytest
from pytest_bdd import scenario


@pytest.fixture
def pytestbdd_feature_base_dir():
    return '/home/user/projects/foo.bar/features'

test_publish = scenario('publish_article.feature', 'Publishing the article')

Subplugins

The pytest BDD has plugin support, and the main purpose of plugins (subplugins) is to provide useful and specialized fixtures.

List of known subplugins:

*  pytest-bdd-splinter -- collection of fixtures for the real browser BDD testing

License

This software is licensed under the MIT license.

© 2013 Oleg Pidsadnyi

Changelog

0.5.2

• Added extra info into output when FeatureError exception raises. (amakhnach)

0.5.0

• Added parametrization to scenarios

• Coveralls.io integration

• Test coverage improvement/fixes

• Correct wrapping of step functions to preserve function docstring

0.4.7

• Fixed Python 3.3 support

0.4.6

• Fixed a bug when py.test –fixtures showed incorrect filenames for the steps.

0.4.5

• Fixed a bug with the reuse of the fixture by given steps being evaluated multiple times.

0.4.3

• Update the license file and PYPI related documentation.