ViewModelで実行されるコルーチンのテスト。 UIStateの変化を見る

ExampleViewModel.kt

package com.example.myapplication

import androidx.lifecycle.SavedStateHandle
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch
import kotlin.random.Random

class ExampleUseCase {
    suspend fun getValue(): Int {
        delay(1500)
        return Random.nextInt(0, 100)
    }
}

class ExampleViewModel(savedStateHandle: SavedStateHandle, private val useCase: ExampleUseCase) :
    ViewModel() {

    private val _uiState = MutableStateFlow(UIState.INIT)
    val uiState = _uiState.asStateFlow()

    private val _value1 = SavableMutableSaveStateFlow(savedStateHandle, "value1", 0)
    val value1 = _value1.asStateFlow()

    enum class UIState {
        INIT,
        LOADING,
        SUCCESS
    }

    fun process() {
        viewModelScope.launch(Dispatchers.IO) {
            _uiState.value = UIState.LOADING
            _value1.value = useCase.getValue()
            _uiState.value = UIState.SUCCESS
        }
    }
}

ExampleViewModelTest.kt

package com.example.myapplication

import com.example.myapplication.ExampleViewModel.UIState
import androidx.arch.core.executor.testing.InstantTaskExecutorRule
import androidx.lifecycle.SavedStateHandle
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.first
import kotlinx.coroutines.test.resetMain
import kotlinx.coroutines.test.runTest
import kotlinx.coroutines.test.setMain
import org.junit.After
import org.junit.Assert.*
import org.junit.Before
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

@ExperimentalCoroutinesApi
@RunWith(JUnit4::class)
class ExampleViewModelTest {

    @get:Rule
    val instantTaskExecutorRule = InstantTaskExecutorRule()

    @Before
    fun setUp() {
        Dispatchers.setMain(Dispatchers.Unconfined)
    }

    @After
    fun tearDown() {
        Dispatchers.resetMain()
    }

    @Test
    fun test1() = runTest {
        val savedStateHandle = SavedStateHandle()
        val useCase = ExampleUseCase()
        val viewModel = ExampleViewModel(savedStateHandle, useCase)

        viewModel.process()

        assertEquals(UIState.LOADING, viewModel.uiState.first())

        while (viewModel.uiState.first() != UIState.SUCCESS) {
            delay(100)
        }
        assertEquals(UIState.SUCCESS, viewModel.uiState.first())
    }
}