Kotlin Mockk test for suspend cancellable coroutine cancellation - unit-testing

Question

I have classes
// final class from some library like okhttp
class NetworkCaller {
fun call() {
// performs some real operation
}
fun cancel() {
// .... cancels the request
}
}
class Request {
suspend fun asyncRequest(): String = suspendCancellableCoroutine { continuation ->
val call = NetworkCaller()
continuation.invokeOnCancellation {
call.cancel() // i need to write a test to mock if call.cancel is getting called or not
}
// rest of the code...
}
}
When i am doing
#Test
fun testRequestCancellation() {
val request = Request()
val job = GlobalScope.launch {
val response = request.asyncRequest()
println(response)
}
runBlocking {
job.cancel()
job.join()
}
}
The job is getting cancelled and continuation.invokeOnCancellation() is getting called, i checked with println statements. But i want to mock if the call.cancel method is getting called or not, using mockk library.
I am stuck on this, need help.

Answer 1

In your class, expose the NetworkCaller so it can be switched out for a mock during testing:
class Request(val call: NetworkCaller = NetworkCaller()) {
suspend fun asyncRequest(): String = suspendCancellableCoroutine { continuation ->
continuation.invokeOnCancellation {
call.cancel() // i need to write a test to mock if call.cancel is getting called or not
}
// rest of the code...
}
}
Then you can use mockk in your test:
#Test
fun testRequestCancellation() {
val mockkCall = mockk<NetworkCaller> {
coEvery { cancel() } just Runs
}
val request = Request(mockkCall)
val job = GlobalScope.launch {
val response = request.asyncRequest()
println(response)
}
runBlocking {
job.cancel()
job.join()
}
coVerify { mockkCall.cancel() }
confirmVerified(mockkCall)
}