Add tests to find pytest fixtures from external plugins

test/examples/pytest_plugin_package/pytest_plugin/fixtures.py

@@ -0,0 +1,6 @@
+from pytest import fixture
+
+
+@fixture()
+def admin_user():
+    pass

test/examples/pytest_plugin_package/pytest_plugin/plugin.py

@@ -0,0 +1,18 @@
+import pytest
+from pytest import fixture
+
+
+from pytest_plugin.fixtures import admin_user  # noqa
+
+
+class Client:
+    def login(self, **credentials):
+        ...
+
+    def logout(self):
+        ...
+
+
+@pytest.fixture()
+def admin_client():
+    return Client()