BDD for pytest
Project description
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
Changes between 0.4.7 and 0.5.0
Added parametrization to scenarios
Coveralls.io integration
Test coverage improvement/fixes
Correct wrapping of step functions to preserve function docstring
Changes between 0.4.6 and 0.4.7
Fixed Python 3.3 support
Changes between 0.4.5 and 0.4.6
Fixed a bug when py.test –fixtures showed incorrect filenames for the steps.
Changes between 0.4.3 and 0.4.5
Fixed a bug with the reuse of the fixture by given steps being evaluated multiple times.
Changes between 0.4.1 and 0.4.3
Update the license file and PYPI related documentation.
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