How to simulate ExoPlayer in unit tests ?

[thibseisel]

[REQUIRED] Searched documentation and issues

• Test projects in ExoPlayer sources : testutils and testutils_robolectric.
• Issue #6267 - Request to publish testutils and testutils_robolectric as artifacts
• Issue #6161 - Design document of new playlist API for ExoPlayer

[REQUIRED] Question

I am using ExoPlayer to play audio with a background service controlled via a Media Session. Since I am doing TDD, I'd like to cover most code with unit and integration tests. I have an ExoPlayer instance that is injected into my service components with Dagger 2, so that any class that communicates with the player has it as a constructor parameter.

Here is my question : how should I mock/fake ExoPlayer, so that I can test components that use it in isolation ? I know that ExoPlayer is an interface and therefore can be mocked with any mocking framework but this only works for simple interactions and mocking Player.EventListener callbacks is rather hard. For that purpose, something like a FakeExoPlayer seems more appropriate.

What I need is a FakeExoPlayer, or a SimpleExoPlayer with fake components that:

• prepares real media sources, but does not actually fetch and play them,
• dispatches Player.EventListener events immediately on the test thread,
• reacts to changes to a ConcatenatedMediaSource.

Here are some things I thought of to solve the question:

• Create my own fake implementation of ExoPlayer, dispatching Player.EventListener events to observers myself in prepare, seekTo, setPlayWhenReady methods. That's a lot of work and it's not ensured to have the same behavior as a real ExoPlayer implementation (don't mock classes you don't own !).
• Use fake components from testutils projects. While those components looks really helpful in testing ExoPlayer itself, I struggle to find how to use them for my use case, i.e. simulating ExoPlayer behavior to test an external component.
• By injecting a fake DataSource.Factory, I'd be able to produce fake MediaSources to feed the ConcatenatingMediaSource created in player preparation code. I think the new Playlist API described in #6161 should make it easier to test media playlist use cases.

Big thanks in advance.

[marcbaechinger]

We are having a bunch of such tests in ExoPlayerTest.

It uses the ExoPlayerTestRunner from thes testutil module you are mentioning above. The test runner internally creates a TestExoPlayer which extends from SimpleExoPlayer.

The test ExoPlayer instance can be wired up with various FakeXYZ components.

To trigger events you can set up a ActionSchedule (see ExoPlayerTest for examples) which issues call to the ExoPlayer instance. Your test asserts can then verify whether a given state has been changed or whether expected methods have been called.

[tonihei]

The general approach should be as Marc described above. Please have a look at our ExoPlayerTestRunner/ExoPlayerTest/ActionSchedule classes to see how this can be done.

More specific comments:

dispatches Player.EventListener events immediately on the test thread,

This approach is using a real player. So all events are dispatched exactly the same way as in non-test cases.

reacts to changes to a ConcatenatedMediaSource

There is no issue with using ConcatenatingMediaSource in a testing scenario or such a test runner.

prepares real media sources, but does not actually fetch and play them

That one is not that easy to solve. We usually use some kind of FakeMediaSource or FakeAdaptiveMediaSource for test purposes. Using actual media sources is problematic because they expect actual media data to work correctly. You can use the real media source If you can provide actual data in the test. Then you could inject a custom DataSource that emits this data and everything should work fine.

[marcbaechinger]

Closing due to lack of activity.