start method
Initializes a test application and starts it.
Runs all before initializers, starts the application under test, and then runs all after initializers.
Prefer to use install instead of calling this method manually.
Implementation
Future start() async {
Controller.letUncaughtExceptionsEscape = true;
_application = Application<T>()..options = options;
await beforeStart();
await application!.startOnCurrentIsolate();
agent = Agent(application);
await afterStart();
}