Docs on temporary plugins in fixtures, closes #2234

docs/testing_plugins.rst

@@ -313,3 +313,19 @@ When writing tests for plugins you may find it useful to register a test plugin
             assert response.status_code == 500
         finally:
             pm.unregister(name="undo")
+
+To reuse the same temporary plugin in multiple tests, you can register it inside a fixture in your ``conftest.py`` file like this:
+
+.. literalinclude:: ../tests/test_docs_plugins.py
+   :language: python
+   :start-after: # -- start datasette_with_plugin_fixture --
+   :end-before: # -- end datasette_with_plugin_fixture --
+
+Note the ``yield`` statement here - this ensures that the ``finally:`` block that unregisters the plugin is executed only after the test function itself has completed.
+
+Then in a test:
+
+.. literalinclude:: ../tests/test_docs_plugins.py
+   :language: python
+   :start-after: # -- start datasette_with_plugin_test --
+   :end-before: # -- end datasette_with_plugin_test --

tests/test_docs_plugins.py

@@ -0,0 +1,34 @@
+# fmt: off
+# -- start datasette_with_plugin_fixture --
+from datasette import hookimpl
+from datasette.app import Datasette
+from datasette.plugins import pm
+import pytest
+import pytest_asyncio
+
+
+@pytest_asyncio.fixture
+async def datasette_with_plugin():
+    class TestPlugin:
+        __name__ = "TestPlugin"
+
+        @hookimpl
+        def register_routes(self):
+            return [
+                (r"^/error$", lambda: 1 / 0),
+            ]
+
+    pm.register(TestPlugin(), name="undo")
+    try:
+        yield Datasette()
+    finally:
+        pm.unregister(name="undo")
+# -- end datasette_with_plugin_fixture --
+
+
+# -- start datasette_with_plugin_test --
+@pytest.mark.asyncio
+async def test_error(datasette_with_plugin):
+    response = await datasette_with_plugin.client.get("/error")
+    assert response.status_code == 500
+# -- end datasette_with_plugin_test --