Android Writing UI tests - Android IdlingResource
Example
The power of idling resources lies in not having to wait for some app's processing (networking, calculations, animations, etc.) to finish with sleep(), which brings flakiness and/or prolongs the tests run. The official documentation can be found here.
Implementation
There are three things that you need to do when implementing IdlingResource interface:
getName()- Returns the name of your idling resource.isIdleNow()- Checks whether your xyz object, operation, etc. is idle at the moment.registerIdleTransitionCallback(IdlingResource.ResourceCallbackcallback) - Provides a callback which you should call when your object transitions to idle.
Now you should create your own logic and determine when your app is idle and when not, since this is dependant on the app. Below you will find a simple example, just to show how it works. There are other examples online, but specific app implementation brings to specific idling resource implementations.
NOTES
- There have been some Google examples where they put
IdlingResourcesin the code of the app. Do not do this. They presumably placed it there just to show how they work. - Keeping your code clean and maintaining single principle of responsibility is up to you!
Example
Let us say that you have an activity which does weird stuff and takes a long time for the fragment to load and thus making your Espresso tests fail by not being able to find resources from your fragment (you should change how your activity is created and when to speed it up). But in any case to keep it simple, the following example shows how it should look like.
Our example idling resource would get two objects:
- The tag of the fragment which you need to find and waiting to get attached to the activity.
- A FragmentManager object which is used for finding the fragment.
/**
* FragmentIdlingResource - idling resource which waits while Fragment has not been loaded.
*/
public class FragmentIdlingResource implements IdlingResource {
private final FragmentManager mFragmentManager;
private final String mTag;
//resource callback you use when your activity transitions to idle
private volatile ResourceCallback resourceCallback;
public FragmentIdlingResource(FragmentManager fragmentManager, String tag) {
mFragmentManager = fragmentManager;
mTag = tag;
}
@Override
public String getName() {
return FragmentIdlingResource.class.getName() + ":" + mTag;
}
@Override
public boolean isIdleNow() {
//simple check, if your fragment is added, then your app has became idle
boolean idle = (mFragmentManager.findFragmentByTag(mTag) != null);
if (idle) {
//IMPORTANT: make sure you call onTransitionToIdle
resourceCallback.onTransitionToIdle();
}
return idle;
}
@Override
public void registerIdleTransitionCallback(ResourceCallback resourceCallback) {
this.resourceCallback = resourceCallback;
}
}
Now that you have your IdlingResource written, you need to use it somewhere right?
Usage
Let us skip the entire test class setup and just look how a test case would look like:
@Test
public void testSomeFragmentText() {
mActivityTestRule.launchActivity(null);
//creating the idling resource
IdlingResource fragmentLoadedIdlingResource = new FragmentIdlingResource(mActivityTestRule.getActivity().getSupportFragmentManager(), SomeFragmentText.TAG);
//registering the idling resource so espresso waits for it
Espresso.registerIdlingResources(idlingResource1);
onView(withId(R.id.txtHelloWorld)).check(matches(withText(helloWorldText)));
//lets cleanup after ourselves
Espresso.unregisterIdlingResources(fragmentLoadedIdlingResource);
}
Combination with JUnit rule
This is not to hard; you can also apply the idling resource in form of a JUnit test rule. For example, let us say that you have some SDK that contains Volley in it and you want Espresso to wait for it. Instead of going through each test case or applying it in setup, you could create a JUnit rule and just write:
@Rule
public final SDKIdlingRule mSdkIdlingRule = new SDKIdlingRule(SDKInstanceHolder.getInstance());
Now since this is an example, don't take it for granted; all code here is imaginary and used only for demonstration purposes:
public class SDKIdlingRule implements TestRule {
//idling resource you wrote to check is volley idle or not
private VolleyIdlingResource mVolleyIdlingResource;
//request queue that you need from volley to give it to idling resource
private RequestQueue mRequestQueue;
//when using the rule extract the request queue from your SDK
public SDKIdlingRule(SDKClass sdkClass) {
mRequestQueue = getVolleyRequestQueue(sdkClass);
}
private RequestQueue getVolleyRequestQueue(SDKClass sdkClass) {
return sdkClass.getVolleyRequestQueue();
}
@Override
public Statement apply(final Statement base, Description description) {
return new Statement() {
@Override
public void evaluate() throws Throwable {
//registering idling resource
mVolleyIdlingResource = new VolleyIdlingResource(mRequestQueue);
Espresso.registerIdlingResources(mVolleyIdlingResource);
try {
base.evaluate();
} finally {
if (mVolleyIdlingResource != null) {
//deregister the resource when test finishes
Espresso.unregisterIdlingResources(mVolleyIdlingResource);
}
}
}
};
}
}
