Simple way to test asynchronous actions in Android: Service, AsyncTask, Thread, RxJava etc.

Sometimes testing asynchronous actions might be very difficult but in most common cases during Android development it might be done with a very simple technique.

If you know basics of concurrency you can test asynchronous operations with a simple wait/notify.

The task:

There is a “Login Activity” with a simple login form and an asynchronous request to the server. Request is performed by IntentService in a background. Result is delivered with broadcast.

Create a test if login is working correctly.

This is a code of our LoginActivity:

1. After pressing “Perform Login” button service starts and performs login in background. Response will be sent with a broadcast. The “action” of a result broadcast is also passed to the service.
2. In the “LoginActivity” the broadcast receiver is registered to listen for the response from the service.
3. When response is received the handleLoginResponse method is called.

Here is the relevant code:

To write a test we need to do a few things:

1. Create LoginTestActivity that extends LoginActivity and override handleResponse method. When this method is called it means that response is received.
2. No need to have this LoginTestActivity in production code that why we create a separate build flavor for testing.
3. Define LoginTestActivity in AndroidManifest.xml of the separate flavor.
4. Create the actual test.

LoginTestActivity is very simple:

This is how our project three looks like with a separate flavor:

And here is the actual test:

1. It enters login and password into appropriate fields
2. Presses “Perform login” button.
3. Waits for asynchronous response with a simple wait/notify.

You should notice the important wait/notify calls.

Because Tests are running in a thread different from main we can easily call

synchronized(syncObject){
    syncObject.wait();
}

When response from LoginService arrives, our LoginTestActivity calls onHandleResponseCalled and here we can notify the syncObject.

Note: we use the Service to perform asynchronous operation. This technique can be used with any asynchronous operation: AsyncTask, Thread, RxJava.

And that’s it. Very simple

All the relevant code is on GitHub

Cheers :)