pytest-bdd 2.5.0

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

An example test for a blog hosting software could look like this. Note that pytest-splinter is used to get the browser fixture.

publish_article.feature:

Feature: Blog
    A site where you can publish your articles.

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

@scenario('publish_article.feature', 'Publishing the article')
def test_publish():
    pass


@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 arguments

Often it’s possible to reuse steps giving them a parameter(s). This allows to have single implementation and multiple use, so less code. Also opens the possibility to use same step twice in single scenario and with different arguments! Important thing that argumented step names are not just strings but regular expressions.

Example:

Scenario: Arguments for given, when, thens
    Given there are 5 cucumbers

    When I eat 3 cucumbers
    And I eat 2 cucumbers

    Then I should have 0 cucumbers

The code will look like:

import re
from pytest_bdd import scenario, given, when, then


@scenario('arguments.feature', 'Arguments for given, when, thens')
def test_arguments():
    pass


@given(re.compile('there are (?P<start>\d+) cucumbers'), converters=dict(start=int))
def start_cucumbers(start):
    return dict(start=start, eat=0)


@when(re.compile('I eat (?P<eat>\d+) cucumbers'), converters=dict(eat=int))
def eat_cucumbers(start_cucumbers, eat):
    start_cucumbers['eat'] += eat


@then(re.compile('I should have (?P<left>\d+) cucumbers'), converters=dict(left=int))
def should_have_left_cucumbers(start_cucumbers, start, left):
    assert start_cucumbers['start'] == start
    assert start - start_cucumbers['eat'] == left

Example code also shows possibility to pass argument converters which may be useful if you need argument types different than strings.

Multiline steps

As Gherkin, pytest-bdd supports multiline steps (aka PyStrings). But in much cleaner and powerful way:

Scenario: Multiline step using sub indentation
    Given I have a step with:
        Some
        Extra
        Lines
    Then the text should be parsed with correct indentation

Step is considered as multiline one, if the next line(s) after it’s first line, is indented relatively to the first line. The step name is then simply extended by adding futher lines with newlines. In the example above, the Given step name will be:

"""I have a step with:\nSome\nExtra\nLines"""

You can of course register step using full name (including the newlines), but it seems more practical to use step arguments and capture lines after first line (or some subset of them) into the argument:

import re

from pytest_bdd import given, then, scenario


@scenario(
    'multiline.feature',
    'Multiline step using sub indentation',
)
def test_multiline():
    pass


@given(re.compile(r'I have a step with:\n(?P<text>.+)', re.DOTALL))
def i_have_text(text):
    return text


@then('the text should be parsed with correct indentation')
def eat_cucumbers(i_have_text, text):
    assert i_have_text == text == """Some
Extra
Lines"""

Pay attention to the re.DOTALL option used for step registration. When used, .+ will also capture newlines.

Scenario parameters

Scenario decorator can accept such optional keyword arguments:

• encoding - decode content of feature file in specific encoding. UTF-8 is default.

• example_converters - mapping to pass functions to convert example values provided in feature files.

Scenario outlines

Scenarios can be parametrized to cover few cases. In Gherkin the variable templates are written using corner braces as <somevalue>. Scenario outlines are supported by pytest-bdd exactly as it’s described in be behave docs.

Example:

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

    Examples:
    | start | eat | left |
    |  12   |  5  |  7   |

pytest-bdd feature file format also supports example tables in different way:

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

    Examples: Vertical
    | start | 12 | 2 |
    | eat   | 5  | 1 |
    | left  | 7  | 1 |

This form allows to have tables with lots of columns keeping the maximum text width predictable without significant readability change.

The code will look like:

from pytest_bdd import given, when, then, scenario


@scenario(
    'outline.feature',
    'Outlined given, when, thens',
    example_converters=dict(start=int, eat=float, left=str)
)
def test_outlined():
    pass


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


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


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

Example code also shows possibility to pass example converters which may be useful if you need parameter types different than strings.

It’s also possible to parametrize the scenario on the python side. The reason for this is that it is sometimes not needed to mention example table for every scenario.

The code will look like:

import pytest
from pytest_bdd import mark, given, when, then


# Here we use pytest to parametrize the test with the parameters table
@pytest.mark.parametrize(
    ['start', 'eat', 'left'],
    [(12, 5, 7)])
@mark.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

The significant downside of this approach is inability to see the test table from the feature file.

Organizing your scenarios

The more features and scenarios you have, the more important becomes the question about their organization. The things you can do (and that is also a recommended way):

• organize your feature files in the folders by semantic groups:

features
│
├──frontend
│  │
│  └──auth
│     │
│     └──login.feature
└──backend
   │
   └──auth
      │
      └──login.feature

This looks fine, but how do you run tests only for certain feature? As pytest-bdd uses pytest, and bdd scenarios are actually normal tests. But test files are separate from the feature files, the mapping is up to developers, so the test files structure can look completely different:

tests
│
└──functional
   │
   └──test_auth.py
      │
      └ """Authentication tests."""
        from pytest_bdd import scenario

        @scenario('frontend/auth/login.feature')
        def test_logging_in_frontend():
            pass

        @scenario('backend/auth/login.feature')
        def test_logging_in_backend():
            pass

For picking up tests to run we can use tests selection technique. The problem is that you have to know how your tests are organized, knowing ony the feature files organization is not enough. cucumber tags introduce standard way of categorizing your features and scenarios, which pytest-bdd supports. For example, we could have:

@login @backend
Feature: Login

  @successful
  Scenario: Successful login

pytest-bdd uses pytest markers as a storage of the tags for the given scenario test, so we can use standard test selection:

py.test -k "@backend and @login and @successful"

The @ helps to separate normal markers from the bdd ones. Note that if you use pytest –strict option, all bdd tags mentioned in the feature files should be also in the markers setting of the pytest.ini config.

Test setup

Test setup is implemented within the Given section. Even though these steps are executed imperatively to apply possible side-effects, pytest-bdd is trying to benefit of the PyTest fixtures which is based on the dependency injection and makes the setup more declarative style.

@given('I have a beautiful article')
def article():
    return Article(is_beautiful=True)

This also declares a PyTest fixture “article” and any other step can depend on it.

Given I have a beautiful article
When I publish this article

When step is referring the article to publish it.

@when('I publish this article')
def publish_article(article):
    article.publish()

Many other BDD toolkits operate a global context and put the side effects there. This makes it very difficult to implement the steps, because the dependencies appear only as the side-effects in the run-time and not declared in the code. The publish article step has to trust that the article is already in the context, has to know the name of the attribute it is stored there, the type etc.

In pytest-bdd you just declare an argument of the step function that it depends on and the PyTest will make sure to provide it.

Still side effects can be applied in the imperative style by design of the BDD.

Given I have a beautiful article
And my article is published

Functional tests can reuse your fixture libraries created for the unit-tests and upgrade them by applying the side effects.

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

@given('my article is published')
def published_article(article):
    article.publish()
    return article

This way side-effects were applied to our article and PyTest makes sure that all steps that require the “article” fixture will receive the same object. The value of the “published_article” and the “article” fixtures is the same object.

Fixtures are evaluated only once within the PyTest scope and their values are cached. In case of Given steps and the step arguments mentioning the same given step makes no sense. It won’t be executed second time.

Given I have a beautiful article
And some other thing
And I have a beautiful article  # Won't be executed, exception is raised

pytest-bdd will raise an exception even in the case of the steps that use regular expression patterns to get arguments.

Given I have 1 cucumbers
And I have 2 cucumbers  # Exception is raised

Will raise an exception if the step is using the regular expression pattern.

@given(re.compile('I have (?P<n>\d+) cucumbers'))
def cucumbers(n):
    return create_cucumbers(n)

Backgrounds

It’s often the case that to cover certain feature, you’ll need multiple scenarios. And it’s logical that the setup for those scenarios will have some common parts (if not equal). For this, there are backgrounds. pytest-bdd implements gherkin backgrounds for features.

Feature: Multiple site support

  Background:
    Given a global administrator named "Greg"
    And a blog named "Greg's anti-tax rants"
    And a customer named "Wilson"
    And a blog named "Expensive Therapy" owned by "Wilson"

  Scenario: Wilson posts to his own blog
    Given I am logged in as Wilson
    When I try to post to "Expensive Therapy"
    Then I should see "Your article was published."

  Scenario: Greg posts to a client's blog
    Given I am logged in as Greg
    When I try to post to "Expensive Therapy"
    Then I should see "Your article was published."

In this example, all steps from the background will be executed before all the scenario’s own given steps, adding possibility to prepare some common setup for multiple scenarios in a single feature. About background best practices, please read here.

Reusing 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')

Reusing 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:

@scenario('common_steps.feature', 'All steps are declared in the conftest')
def test_conftest():
    pass

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

Using unicode in the feature files

As mentioned above, by default, utf-8 encoding is used for parsing feature files. For steps definition, you can both use unicode- and bytestrings equally. However, for argumented steps, if you need to use unicode symbols in it’s regular expression, use u sign with regex:

@given(re.compile(u"у мене є рядок який містить '{0}'".format('(?P<content>.+)')))
def there_is_a_string_with_content(content, string):
    """Create string with unicode content."""
    string['content'] = content

Default steps

Here is the list of steps that are implemented inside of the pytest-bdd:

given

• trace - enters the pdb debugger via pytest.set_trace()

when

• trace - enters the pdb debugger via pytest.set_trace()

then

• trace - enters the pdb debugger via pytest.set_trace()

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'


@scenario('publish_article.feature', 'Publishing the article')
def test_publish():
    pass

Avoid retyping the feature file name

If you want to avoid retyping the feature file name when defining your scenarios in a test file, use functools.partial. This will make your life much easier when defining multiple scenarios in a test file.

For example:

test_publish_article.py:

from functools import partial

import pytest_bdd


scenario = partial(pytest_bdd.scenario, '/path/to/publish_article.feature')


@scenario('Publishing the article')
def test_publish():
    pass


@scenario('Publishing the article as unprivileged user')
def test_publish_unprivileged():
    pass

You can learn more about functools.partial in the Python docs.

Hooks

pytest-bdd exposes several pytest hooks which might be helpful building useful reporting, visualization, etc on top of it:

• pytest_bdd_before_step(request, feature, scenario, step, step_func) - Called before step function is executed and it’s arguments evaluated

• pytest_bdd_after_step(request, feature, scenario, step, step_func, step_func_args) - Called after step function is successfully executed

• pytest_bdd_step_error(request, feature, scenario, step, step_func, step_func_args, exception) - Called when step function failed to execute

• pytest_bdd_step_validation_error(request, feature, scenario, step, step_func, step_func_args, exception) - Called when step failed to validate

• pytest_bdd_step_func_lookup_error(request, feature, scenario, step, exception) - Called when step lookup failed

Browser testing

Tools recommended to use for browser testing:

• pytest-splinter - pytest splinter integration for the real browser testing

Reporting

It’s important to have nice reporting out of your bdd tests. Cucumber introduced some kind of standard for json format which can be used for this jenkins plugin

To have an output in json format:

py.test --cucumberjson=<path to json report>

Test code generation helpers

For newcomers it’s sometimes hard to write all needed test code without being frustrated. To simplify their life, simple code generator was implemented. It allows to create fully functional but of course empty tests and step definitions for given a feature file. It’s done as a separate console script provided by pytest-bdd package:

pytest-bdd generate <feature file name> .. <feature file nameN>

It will print the generated code to the standard output so you can easily redirect it to the file:

pytest-bdd generate features/some.feature > tests/functional/test_some.py

Advanced code generation

For more experienced users, there’s smart code generation/suggestion feature. It will only generate the test code which is not yet there, checking existing tests and step definitions the same way it’s done during the test execution. The code suggestion tool is called via passing additional pytest arguments:

py.test --generate-missing --feature features tests/functional

The output will be like:

============================= test session starts ==============================
platform linux2 -- Python 2.7.6 -- py-1.4.24 -- pytest-2.6.2
plugins: xdist, pep8, cov, cache, bdd, bdd, bdd
collected 2 items

Scenario is not bound to any test: "Code is generated for scenarios which are not bound to any tests" in feature "Missing code generation" in /tmp/pytest-552/testdir/test_generate_missing0/tests/generation.feature
--------------------------------------------------------------------------------

Step is not defined: "I have a custom bar" in scenario: "Code is generated for scenario steps which are not yet defined(implemented)" in feature "Missing code generation" in /tmp/pytest-552/testdir/test_generate_missing0/tests/generation.feature
--------------------------------------------------------------------------------
Please place the code above to the test file(s):

@scenario('tests/generation.feature', 'Code is generated for scenarios which are not bound to any tests')
def test_Code_is_generated_for_scenarios_which_are_not_bound_to_any_tests():
    """Code is generated for scenarios which are not bound to any tests."""


@given('I have a custom bar')
def I_have_a_custom_bar():
    """I have a custom bar."""

As as side effect, the tool will validate the files for format errors, also some of the logic bugs, for example the ordering of the types of the steps.

Migration of your tests from versions 0.x.x-1.x.x

In version 2.0.0, the backwards-incompartible change was introduced: scenario function can now only be used as a decorator. Reasons for that:

• test code readability is much higher using normal python function syntax;

• pytest-bdd internals are much cleaner and shorter when using single approach instead of supporting two;

• after moving to parsing-on-import-time approach for feature files, it’s not possible to detect whether it’s a decorator more or not, so to support it along with functional approach there needed to be special parameter for that, which is also a backwards-incompartible change.

To help users migrate to newer version, there’s migration subcommand of the pytest-bdd console script:

# run migration script
pytest-bdd migrate <your test folder>

Under the hood the script does the replacement from this:

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

to this:

@scenario('publish_article.feature', 'Publishing the article')
def test_function():
    pass

License

This software is licensed under the MIT license.

© 2013 Oleg Pidsadnyi

Changelog

2.5.0

• Fix multiline steps in the Background section (bubenkoff, arpe)

• Code cleanup (olegpidsadnyi)

2.4.5

• Fix unicode issue with scenario name (bubenkoff, aohontsev)

2.4.3

• Fix unicode regex argumented steps issue (bubenkoff, aohontsev)

• Fix steps timings in the json reporting (bubenkoff)

2.4.2

• Recursion is fixed for the –generate-missing and the –feature parameters (bubenkoff)

2.4.1

• Better reporting of a not found scenario (bubenkoff)

• Simple test code generation implemented (bubenkoff)

• Correct timing values for cucumber json reporting (bubenkoff)

• Validation/generation helpers (bubenkoff)

2.4.0

• Background support added (bubenkoff)

• Fixed double collection of the conftest files if scenario decorator is used (ropez, bubenkoff)

2.3.3

• Added timings to the cucumber json report (bubenkoff)

2.3.2

• Fixed incorrect error message using e.argname instead of step.name (hvdklauw)

2.3.1

• Implemented cucumber tags support (bubenkoff)

• Implemented cucumber json formatter (bubenkoff, albertjan)

• Added ‘trace’ keyword (bubenkoff)

2.1.2

• Latest pytest compartibility fixes (bubenkoff)

2.1.1

• Bugfixes (bubenkoff)

2.1.0

• Implemented multiline steps (bubenkoff)

2.0.1

• Allow more than one parameter per step (bubenkoff)

• Allow empty example values (bubenkoff)

2.0.0

• Pure pytest parametrization for scenario outlines (bubenkoff)

• Argumented steps now support converters (transformations) (bubenkoff)

• scenario supports only decorator form (bubenkoff)

• Code generation refactoring and cleanup (bubenkoff)

1.0.0

• Implemented scenario outlines (bubenkoff)

0.6.11

• Fixed step arguments conflict with the fixtures having the same name (olegpidsadnyi)

0.6.9

• Implemented support of Gherkin “Feature:” (olegpidsadnyi)

0.6.8

• Implemented several hooks to allow reporting/error handling (bubenkoff)

0.6.6

• Fixes to unnecessary mentioning of pytest-bdd package files in py.test log with -v (bubenkoff)

0.6.5

• Compartibility with recent pytest (bubenkoff)

0.6.4

• More unicode fixes (amakhnach)

0.6.3

• Added unicode support for feature files. Removed buggy module replacement for scenario. (amakhnach)

0.6.2

• Removed unnecessary mention of pytest-bdd package files in py.test log with -v (bubenkoff)

0.6.1

• Step arguments in whens when there are no given arguments used. (amakhnach, bubenkoff)

0.6.0

• Added step arguments support. (curzona, olegpidsadnyi, bubenkoff)

• Added checking of the step type order. (markon, olegpidsadnyi)

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.