Remove app instance from Config for error handler setting (#2320)

tests/test_errorpages.py

@@ -280,40 +280,20 @@ def test_allow_fallback_error_format_set_main_process_start(app):
     async def start(app, _):
         app.config.FALLBACK_ERROR_FORMAT = "text"
 
-    request, response = app.test_client.get("/error")
-    assert request.app.error_handler.fallback == "text"
+    _, response = app.test_client.get("/error")
     assert response.status == 500
     assert response.content_type == "text/plain; charset=utf-8"
 
 
-def test_setting_fallback_to_non_default_raise_warning(app):
-    app.error_handler = ErrorHandler(fallback="text")
+def test_setting_fallback_on_config_changes_as_expected(app):
+    app.error_handler = ErrorHandler()
 
-    assert app.error_handler.fallback == "text"
-
-    with pytest.warns(
-        UserWarning,
-        match=(
-            "Overriding non-default ErrorHandler fallback value. "
-            "Changing from text to auto."
-        ),
-    ):
-        app.config.FALLBACK_ERROR_FORMAT = "auto"
-
-    assert app.error_handler.fallback == "auto"
+    _, response = app.test_client.get("/error")
+    assert response.content_type == "text/html; charset=utf-8"
 
     app.config.FALLBACK_ERROR_FORMAT = "text"
-
-    with pytest.warns(
-        UserWarning,
-        match=(
-            "Overriding non-default ErrorHandler fallback value. "
-            "Changing from text to json."
-        ),
-    ):
-        app.config.FALLBACK_ERROR_FORMAT = "json"
-
-    assert app.error_handler.fallback == "json"
+    _, response = app.test_client.get("/error")
+    assert response.content_type == "text/plain; charset=utf-8"
 
 
 def test_allow_fallback_error_format_in_config_injection():
@@ -327,7 +307,6 @@ def test_allow_fallback_error_format_in_config_injection():
         raise Exception("something went wrong")
 
     request, response = app.test_client.get("/error")
-    assert request.app.error_handler.fallback == "text"
     assert response.status == 500
     assert response.content_type == "text/plain; charset=utf-8"
 
@@ -339,6 +318,23 @@ def test_allow_fallback_error_format_in_config_replacement(app):
     app.config = MyConfig()
 
     request, response = app.test_client.get("/error")
-    assert request.app.error_handler.fallback == "text"
     assert response.status == 500
     assert response.content_type == "text/plain; charset=utf-8"
+
+
+def test_config_fallback_before_and_after_startup(app):
+    app.config.FALLBACK_ERROR_FORMAT = "json"
+
+    @app.main_process_start
+    async def start(app, _):
+        app.config.FALLBACK_ERROR_FORMAT = "text"
+
+    _, response = app.test_client.get("/error")
+    assert response.status == 500
+    assert response.content_type == "text/plain; charset=utf-8"
+
+
+def test_config_fallback_bad_value(app):
+    message = "Unknown format: fake"
+    with pytest.raises(SanicException, match=message):
+        app.config.FALLBACK_ERROR_FORMAT = "fake"