Fix empty docstring delivery to step functions (#809)

CHANGES.rst

@@ -30,6 +30,7 @@ Removed
 Fixed
 +++++
 * Made type annotations stronger and removed most of the ``typing.Any`` usages and ``# type: ignore`` annotations. `#658 <https://github.com/pytest-dev/pytest-bdd/pull/658>`_
+* Empty docstrings are now correctly forwarded to step functions as an empty string instead of being silently dropped, which previously caused pytest to report a missing ``docstring`` fixture. `#809 <https://github.com/pytest-dev/pytest-bdd/issues/809>`_
 
 Security
 ++++++++

src/pytest_bdd/parser.py

@@ -217,7 +217,7 @@ def render(self, context: Mapping[str, object]) -> Scenario:
                 line_number=step.line_number,
                 keyword=step.keyword,
                 datatable=step.render_datatable(step.datatable, context) if step.datatable else None,
-                docstring=render_string(step.docstring, context) if step.docstring else None,
+                docstring=render_string(step.docstring, context) if step.docstring is not None else None,
             )
             for step in base_steps
         ]

tests/steps/test_docstring.py

@@ -197,6 +197,56 @@ def _():
     result.assert_outcomes(passed=1)
 
 
+def test_steps_with_empty_docstring(pytester):
+    """Regression test for #809.
+
+    An empty docstring must be passed to the step function as an empty
+    string. Before the fix it was dropped, and pytest then treated
+    ``docstring`` as a missing fixture.
+    """
+    pytester.makefile(
+        ".feature",
+        empty_docstring=textwrap.dedent(
+            '''\
+            Feature: Empty docstring
+
+              Scenario: Step receives an empty docstring
+                Given a step has an empty docstring
+                """
+                """
+            '''
+        ),
+    )
+    pytester.makeconftest(
+        textwrap.dedent(
+            r"""
+        from pytest_bdd import given
+        from pytest_bdd.utils import dump_obj
+
+
+        @given("a step has an empty docstring")
+        def _(docstring):
+            dump_obj(docstring)
+            """
+        )
+    )
+    pytester.makepyfile(
+        textwrap.dedent(
+            """\
+            from pytest_bdd import scenarios
+
+            scenarios("empty_docstring.feature")
+            """
+        )
+    )
+
+    result = pytester.runpytest("-s")
+    result.assert_outcomes(passed=1)
+
+    docstrings = collect_dumped_objects(result)
+    assert docstrings == [""]
+
+
 def test_docstring_step_argument_is_reserved_and_cannot_be_used(pytester):
     pytester.makefile(
         ".feature",