Merge pull request #431 from pytest-dev/then-when-target-fixture

Support `target_fixture` in `when` and `then` steps.

CHANGES.rst

@@ -3,6 +3,7 @@ Changelog
 
 Unreleased
 -----------
+- `when` and `then` steps now can provide a `target_fixture`, just like `given` does. Discussion at https://github.com/pytest-dev/pytest-bdd/issues/402.
 - Drop compatibility for python 2 and officially support only python >= 3.6.
 - Fix error when using `--cucumber-json-expanded` in combination with `example_converters` (marcbrossaissogeti).
 - Fix `--generate-missing` not correctly recognizing steps with parsers

README.rst

@@ -359,6 +359,47 @@ it will stay untouched. To allow this, special parameter `target_fixture` exists
 In this example existing fixture `foo` will be overridden by given step `I have injecting given` only for scenario it's
 used in.
 
+Sometimes it is also useful to let `when` and `then` steps to provide a fixture as well.
+A common use case is when we have to assert the outcome of an HTTP request:
+
+.. code-block:: python
+
+    # test_blog.py
+
+    from pytest_bdd import scenarios, given, when, then
+
+    from my_app.models import Article
+
+    scenarios("blog.feature")
+
+
+    @given("there is an article", target_fixture="article")
+    def there_is_an_article():
+        return Article()
+
+
+    @when("I request the deletion of the article", target_fixture="request_result")
+    def there_should_be_a_new_article(article, http_client):
+        return http_client.delete(f"/articles/{article.uid}")
+
+
+    @then("the request should be successful")
+    def article_is_published(request_result):
+        assert request_result.status_code == 200
+
+
+.. code-block:: gherkin
+
+    # blog.feature
+
+    Feature: Blog
+        Scenario: Deleting the article
+            Given there is an article
+
+            When I request the deletion of the article
+
+            Then the request should be successful
+
 
 Multiline steps
 ---------------

pytest_bdd/steps.py

@@ -61,35 +61,37 @@ def given(name, converters=None, target_fixture=None):
     :param name: Step name or a parser object.
     :param converters: Optional `dict` of the argument or parameter converters in form
                        {<param_name>: <converter function>}.
-    :param target_fixture: Target fixture name to replace by steps definition function
+    :param target_fixture: Target fixture name to replace by steps definition function.
 
     :return: Decorator function for the step.
     """
     return _step_decorator(GIVEN, name, converters=converters, target_fixture=target_fixture)
 
 
-def when(name, converters=None):
+def when(name, converters=None, target_fixture=None):
     """When step decorator.
 
     :param name: Step name or a parser object.
     :param converters: Optional `dict` of the argument or parameter converters in form
                        {<param_name>: <converter function>}.
+    :param target_fixture: Target fixture name to replace by steps definition function.
 
     :return: Decorator function for the step.
     """
-    return _step_decorator(WHEN, name, converters=converters)
+    return _step_decorator(WHEN, name, converters=converters, target_fixture=target_fixture)
 
 
-def then(name, converters=None):
+def then(name, converters=None, target_fixture=None):
     """Then step decorator.
 
     :param name: Step name or a parser object.
     :param converters: Optional `dict` of the argument or parameter converters in form
                        {<param_name>: <converter function>}.
+    :param target_fixture: Target fixture name to replace by steps definition function.
 
     :return: Decorator function for the step.
     """
-    return _step_decorator(THEN, name, converters=converters)
+    return _step_decorator(THEN, name, converters=converters, target_fixture=target_fixture)
 
 
 def _step_decorator(step_type, step_name, converters=None, target_fixture=None):

tests/feature/test_steps.py

@@ -1,5 +1,4 @@
 import textwrap
-import pytest
 
 
 def test_steps(testdir):
@@ -73,6 +72,59 @@ def test_steps(testdir):
     result.assert_outcomes(passed=1, failed=0)
 
 
+def test_all_steps_can_provide_fixtures(testdir):
+    """Test that given/when/then can all provide fixtures."""
+    testdir.makefile(
+        ".feature",
+        steps=textwrap.dedent(
+            """\
+            Feature: Step fixture
+                Scenario: Given steps can provide fixture
+                    Given Foo is "bar"
+                    Then foo should be "bar"
+                Scenario: When steps can provide fixture
+                    When Foo is "baz"
+                    Then foo should be "baz"
+                Scenario: Then steps can provide fixture
+                    Then foo is "qux"
+                    And foo should be "qux"
+            """
+        ),
+    )
+
+    testdir.makepyfile(
+        textwrap.dedent(
+            """\
+        from pytest_bdd import given, when, then, parsers, scenarios
+
+        scenarios("steps.feature")
+
+        @given(parsers.parse('Foo is "{value}"'), target_fixture="foo")
+        def given_foo_is_value(value):
+            return value
+
+
+        @when(parsers.parse('Foo is "{value}"'), target_fixture="foo")
+        def when_foo_is_value(value):
+            return value
+
+
+        @then(parsers.parse('Foo is "{value}"'), target_fixture="foo")
+        def then_foo_is_value(value):
+            return value
+
+
+        @then(parsers.parse('foo should be "{value}"'))
+        def foo_is_foo(foo, value):
+            assert foo == value
+
+        """
+        )
+    )
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=3, failed=0)
+
+
 def test_when_first(testdir):
     testdir.makefile(
         ".feature",