JUnit testing for Firebase Realtime Database DataSnapshot with mockk

I try to write tests for async functions that load data from the Firebase Realtime Database.

    suspend fun getUsers(): Resource<GETUsers> =
    try {
        val users = databaseReference.get().await().getValue<GETUsers>()!!
        Resource.Success(users)
    } catch(e: Exception) {
        Resource.Error(e.message ?: Constants.UNKNOWN_ERROR)
    }

I have already written similar tests for the Firebase authorizations which have worked. However, the current test does not return the desired result.

    @Test
fun `getUsers() called should return success with two users`() {
    val user01 = GETUser()
    val user02 = GETUser()
    val user01ID = "exampleUser01ID"
    val user02ID = "exampleUser02ID"
    val users = mutableMapOf(user01ID to user01, user02ID to user02)
    val expectedResult = GETUsers(users)
    val task: Task<DataSnapshot> = mockkTask()
    val snapshot: DataSnapshot = mockk()

    every { databaseReference.get() } returns task
    every { task.result } returns snapshot
    every { snapshot.getValue<GETUsers>()!! } returns expectedResult

    val result = runBlocking { repository.getUsers() }
    println(result)

    Assert.assertTrue(result is Resource.Success)
    Assert.assertEquals(2, (result as Resource.Success).data.users.size)
    Assert.assertEquals(user01, result.data.users[user01ID])
    Assert.assertEquals(user02, result.data.users[user02ID])
}

private inline fun <reified T> mockkTask(exception: Exception? = null): Task<T> {
    val task = mockk<Task<T>>(relaxed = true) {
        every { isComplete } returns true
        every { this@mockk.exception } returns exception
        every { isCanceled } returns false
        every { result } returns mockk(relaxed = true)
    }
    return task
}

I think the error is because the cast to GETUsers does not work correctly, if I print result I get the following displayed:

Error(message=class java.lang.Object cannot be cast to class com.example.social_bike_repair.models.GETUsers (java.lang.Object is in module java.base of loader 'bootstrap'; com.example.social_bike_repair.models.GETUsers is in unnamed module of loader 'app'))

I think I need to change something on this line of the mockkTast function, but I'm not quite sure how.

every { result } returns mockk(relaxed = true)

The problem was that the cast in the code to be tested was incorrect.

I have

val users = databaseReference.get().await().getValue<GETUsers>()!!

amended accordingly

val users = databaseReference.get().await().getValue(GETUsers::class.java)!!

and the test works as intended.

Also I must changed this

every { snapshot.getValue<GETUsers>()!! } returns expectedResult

to this

every { snapshot.getValue(GETUsers::class.java) } returns expectedResult