Add minimal docs for package-scoped fixtures (experimental)

changelog/2283.feature

@@ -1 +1 @@
-Pytest now supports package-level fixtures.
+New ``package`` fixture scope: fixtures are finalized when the last test of a *package* finishes. This feature is considered **experimental**, so use it sparingly.

doc/en/fixture.rst

@@ -258,6 +258,22 @@ instance, you can simply declare it:
 Finally, the ``class`` scope will invoke the fixture once per test *class*.
 
 
+``package`` scope (experimental)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. versionadded:: 3.7
+
+In pytest 3.7 the ``package`` scope has been introduced. Package-scoped fixtures
+are finalized when the last test of a *package* finishes.
+
+.. warning::
+    This functionality is considered **experimental** and may be removed in future
+    versions if hidden corner-cases or serious problems with this functionality
+    are discovered after it gets more usage in the wild.
+
+    Use this new feature sparingly and please make sure to report any issues you find.
+
+
 Higher-scoped fixtures are instantiated first
 ---------------------------------------------
 

src/_pytest/fixtures.py

@@ -960,16 +960,27 @@ def __call__(self, function):
 def fixture(scope="function", params=None, autouse=False, ids=None, name=None):
     """Decorator to mark a fixture factory function.
 
-    This decorator can be used (with or without parameters) to define a
-    fixture function.  The name of the fixture function can later be
-    referenced to cause its invocation ahead of running tests: test
-    modules or classes can use the pytest.mark.usefixtures(fixturename)
-    marker.  Test functions can directly use fixture names as input
+    This decorator can be used, with or without parameters, to define a
+    fixture function.
+
+    The name of the fixture function can later be referenced to cause its
+    invocation ahead of running tests: test
+    modules or classes can use the ``pytest.mark.usefixtures(fixturename)``
+    marker.
+
+    Test functions can directly use fixture names as input
     arguments in which case the fixture instance returned from the fixture
     function will be injected.
 
+    Fixtures can provide their values to test functions using ``return`` or ``yield``
+    statements. When using ``yield`` the code block after the ``yield`` statement is executed
+    as teardown code regardless of the test outcome, and must yield exactly once.
+
     :arg scope: the scope for which this fixture is shared, one of
-                "function" (default), "class", "module" or "session".
+                ``"function"`` (default), ``"class"``, ``"module"``,
+                ``"package"`` or ``"session"``.
+
+                ``"package"`` is considered **experimental** at this time.
 
     :arg params: an optional list of parameters which will cause multiple
                 invocations of the fixture function and all of the tests
@@ -990,10 +1001,6 @@ def fixture(scope="function", params=None, autouse=False, ids=None, name=None):
                 to resolve this is to name the decorated function
                 ``fixture_<fixturename>`` and then use
                 ``@pytest.fixture(name='<fixturename>')``.
-
-    Fixtures can optionally provide their values to test functions using a ``yield`` statement,
-    instead of ``return``. In this case, the code block after the ``yield`` statement is executed
-    as teardown code regardless of the test outcome. A fixture function must yield exactly once.
     """
     if callable(scope) and params is None and autouse is False:
         # direct decoration