curioustechizen / kotlin-coroutines-test-issue

Sample showing problems testing kotlin suspending functions

Objective

Try to write unit tests for a kotlin class that includes suspending functions. In particular,

call a regular function and then verify that it in turn calls a suspending function.

This is a regular desktop Java project that you can run with IntelliJ IDEA

Explanation

In this project, ViewModel has a getGreeting() function which in turn calls a suspending getGreeting() on the Repository. This suspending function simply calls delay() but in real world usage it might do some computation or I/O.

The test that I'm trying to get to work is when ViewModel getGreeting called then it calls repo getGreeting in LogicTest.kt.

The key

I was having problems where Mockito verification was failing - I would see an error saying that the repository getName() suspending function was never called.

The key to fixing it was to share the coroutineContext between runBlocking in my tests and my ViewModel.

This fails:

runBlocking<Unit> {
    verify(repo).getGreeting("")
}

This passes:

runBlocking<Unit>(testCoroutineContext) {
    verify(repo).getGreeting("")
}

See the LogicTest.kt file to see how this context is shared between the test code and the ViewModel