VIEW_MODEL.md

Testing a ViewModel

Setup

When testing a ViewModel we need to check if our ViewModel makes any use of LiveData. In case we do make use of LiveData we need to add the following rule:

@get:Rule
val instantTaskExecutorRule = InstantTaskExecutorRule()

What this rule does, as mentioned in the rule's JavaDoc:

A JUnit Test Rule that swaps the background executor used by the Architecture Components with a different one which executes each task synchronously.

Dependencies

In order to add the dependencies required by our ViewModel, we need to add mocks for the underlying Repository each of the UseCase we depend on, requires.

Test case

The test case still needs to be executed inside a coroutinesRule.testDispatcher.runBlockingTest.

LiveDat testing

If our ViewModel outputs any LiveData we need to make use of observeForTesting extension in order to wait until our LiveData has emitted a value. After the block in observeForTesting has been invoked, we can use LiveData.forceGet to get the value of that LiveData and assert on it.