Config coverage upgrade (#898)

* Small test config up

* Correct indent

tests/test_config.py

@@ -65,12 +65,27 @@ def test_proxy_headers():
     assert isinstance(config.loaded_app, ProxyHeadersMiddleware)
 
 
-def test_app_unimportable():
+def test_app_unimportable_module():
     config = Config(app="no.such:app")
     with pytest.raises(ImportError):
         config.load()
 
 
+def test_app_unimportable_other(caplog):
+    config = Config(app="tests.test_config:app")
+    with pytest.raises(SystemExit):
+        config.load()
+    error_messages = [
+        record.message
+        for record in caplog.records
+        if record.name == "uvicorn.error" and record.levelname == "ERROR"
+    ]
+    assert (
+        'Error loading ASGI app. Attribute "app" not found in module "tests.test_config".'  # noqa: E501
+        == error_messages.pop(0)
+    )
+
+
 def test_app_factory():
     def create_app():
         return asgi_app