Replace AsgiLifespan with AsgiRunOnFirstRequest, refs #1955

docs/plugin_hooks.rst

@@ -902,13 +902,14 @@ Potential use-cases:
 
 .. note::
 
-   If you are writing :ref:`unit tests <testing_plugins>` for a plugin that uses this hook you will need to explicitly call ``await ds.invoke_startup()`` in your tests. An example:
+   If you are writing :ref:`unit tests <testing_plugins>` for a plugin that uses this hook and doesn't exercise Datasette by sending
+   any simulated requests through it you will need to explicitly call ``await ds.invoke_startup()`` in your tests. An example:
 
    .. code-block:: python
 
         @pytest.mark.asyncio
         async def test_my_plugin():
-            ds = Datasette([], metadata={})
+            ds = Datasette()
             await ds.invoke_startup()
             # Rest of test goes here
 

docs/testing_plugins.rst

@@ -80,7 +80,7 @@ Creating a ``Datasette()`` instance like this as useful shortcut in tests, but t
 
 This method registers any :ref:`plugin_hook_startup` or :ref:`plugin_hook_prepare_jinja2_environment` plugins that might themselves need to make async calls.
 
-If you are using ``await datasette.client.get()`` and similar methods then you don't need to worry about this - those method calls ensure that ``.invoke_startup()`` has been called for you.
+If you are using ``await datasette.client.get()`` and similar methods then you don't need to worry about this - Datasette automatically calls ``invoke_startup()`` the first time it handles a request.
 
 .. _testing_plugins_pdb: