refactor: do not run all runners in ipywidgets_runner fixture

Each time the ipywidgets_runner fixture was used, all fixtures
are used. This means the ipywidgets_runner_solara runner was
also used, causing the solara_test fixture to always run
and also close the app each time, which close all the contexts.

This is bad for performance of the tests, but it is possibly also
the cause for some flakeyness in our tests.

solara/test/pytest_plugin.py

@@ -130,12 +130,16 @@ def page_session(context_session: "playwright.sync_api.BrowserContext"):
 
 @pytest.fixture()
 def solara_app(solara_server):
+    used_app = None
+
     @contextlib.contextmanager
     def run(app: Union[solara.server.app.AppScript, str]):
+        nonlocal used_app
         if "__default__" in solara.server.app.apps:
             solara.server.app.apps["__default__"].close()
         if isinstance(app, str):
             app = solara.server.app.AppScript(app)
+        used_app = app
         solara.server.app.apps["__default__"] = app
         try:
             yield
@@ -146,9 +150,9 @@ def run(app: Union[solara.server.app.AppScript, str]):
                 if app.name in reload.reloader.watched_modules:
                     reload.reloader.watched_modules.remove(app.name)
 
-            app.close()
-
-    return run
+    yield run
+    if used_app:
+        used_app.close()
 
 
 run_event = threading.Event()
@@ -165,20 +169,21 @@ def SyncWrapper():
     return w.VBox(children=[w.HTML(value="Test in solara"), w.VBox()])
 
 
-@pytest.fixture()
-def solara_test(solara_server, solara_app, page_session: "playwright.sync_api.Page"):
+@contextlib.contextmanager
+def _solara_test(solara_server, solara_app, page_session: "playwright.sync_api.Page"):
     global run_calls
     with solara_app("solara.test.pytest_plugin:SyncWrapper"):
+        assert len(solara.server.app.contexts) == 0
         page_session.goto(solara_server.base_url)
-        run_event.wait()
-        assert run_calls == 1
-        keys = list(solara.server.app.contexts)
-        assert len(keys) == 1, "expected only one context, got %s" % keys
-        context = solara.server.app.contexts[keys[0]]
-        with context:
-            test_output_warmup = widgets.Output()
-            test_output = widgets.Output()
-            try:
+        try:
+            run_event.wait()
+            assert run_calls == 1
+            keys = list(solara.server.app.contexts)
+            assert len(keys) == 1, "expected only one context, got %s" % keys
+            context = solara.server.app.contexts[keys[-1]]
+            with context:
+                test_output_warmup = widgets.Output()
+                test_output = widgets.Output()
                 page_session.locator("text=Test in solara").wait_for()
                 context.container.children[0].children[1].children[1].children = [test_output_warmup]  # type: ignore
                 with test_output_warmup:
@@ -192,11 +197,16 @@ def solara_test(solara_server, solara_app, page_session: "playwright.sync_api.Pa
                 context.container.children[0].children[1].children[1].children = [test_output]  # type: ignore
                 with test_output:
                     yield
-            finally:
                 test_output.close()
-                run_event.clear()
-                test_output = None
-                run_calls = 0
+        finally:
+            run_calls = 0
+            run_event.clear()
+
+
+@pytest.fixture()
+def solara_test(solara_server, solara_app, page_session: "playwright.sync_api.Page"):
+    with _solara_test(solara_server, solara_app, page_session):
+        yield
 
 
 class ServerVoila(ServerBase):
@@ -436,7 +446,8 @@ def run(f: Callable):
     return run
 
 
-def create_runner_solara(solara_test, solara_server, page_session: "playwright.sync_api.Page"):
+@contextlib.contextmanager
+def create_runner_solara(solara_server, solara_app, page_session: "playwright.sync_api.Page"):
     count = 0
 
     def run(f: Callable):
@@ -455,51 +466,35 @@ def run(f: Callable):
             sys.path.remove(cwd)
         count += 1
 
-    return run
-
-
-@pytest.fixture(scope="session")
-def ipywidgets_runner_voila(voila_server, notebook_path, page_session: "playwright.sync_api.Page"):
-    if "voila" not in runners:
-        return None
-    return create_runner_voila(voila_server, notebook_path, page_session)
-
-
-@pytest.fixture(scope="session")
-def ipywidgets_runner_jupyter_lab(jupyter_server, notebook_path, page_session: "playwright.sync_api.Page"):
-    if "jupyter_lab" not in runners:
-        return None
-    return create_runner_jupyter_lab(jupyter_server, notebook_path, page_session)
-
-
-@pytest.fixture(scope="session")
-def ipywidgets_runner_jupyter_notebook(jupyter_server, notebook_path, page_session: "playwright.sync_api.Page"):
-    if "jupyter_notebook" not in runners:
-        return None
-    return create_runner_jupyter_notebook(jupyter_server, notebook_path, page_session)
-
-
-@pytest.fixture()
-def ipywidgets_runner_solara(solara_test, solara_server, page_session: "playwright.sync_api.Page"):
-    if "solara" not in runners:
-        return None
-    return create_runner_solara(solara_test, solara_server, page_session)
+    with _solara_test(solara_server, solara_app, page_session):
+        yield run
 
 
 runners = os.environ.get("SOLARA_TEST_RUNNERS", "solara,voila,jupyter_lab,jupyter_notebook").split(",")
 
 
 @pytest.fixture(params=runners)
 def ipywidgets_runner(
-    ipywidgets_runner_jupyter_notebook,
-    ipywidgets_runner_jupyter_lab,
-    ipywidgets_runner_voila,
-    ipywidgets_runner_solara,
+    solara_server,
+    solara_app,
+    voila_server,
+    jupyter_server,
+    notebook_path,
+    page_session: "playwright.sync_api.Page",
     request,
 ):
     runner = request.param
-    name = f"ipywidgets_runner_{runner}"
-    return locals()[name]
+    if runner == "solara":
+        with create_runner_solara(solara_server, solara_app, page_session) as runner:
+            yield runner
+    elif runner == "voila":
+        yield create_runner_voila(voila_server, notebook_path, page_session)
+    elif runner == "jupyter_lab":
+        yield create_runner_jupyter_lab(jupyter_server, notebook_path, page_session)
+    elif runner == "jupyter_notebook":
+        yield create_runner_jupyter_notebook(jupyter_server, notebook_path, page_session)
+    else:
+        raise RuntimeError(f"Unknown runner {runner}")
 
 
 @pytest.fixture(scope="session")