Archery Apprentice Documentation

How to Test ViewModels

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How to Test ViewModels

Guide to testing ViewModels with StateFlow and coroutines.

Basic ViewModel Test

class MyViewModelTest {
    private lateinit var viewModel: MyViewModel
    private lateinit var mockRepository: MyRepository
 
    @Before
    fun setup() {
        mockRepository = mockk()
        viewModel = MyViewModel(mockRepository)
    }
 
    @Test
    fun `initial state is correct`() {
        val state = viewModel.uiState.value
 
        assertTrue(state.items.isEmpty())
        assertFalse(state.isLoading)
        assertNull(state.error)
    }
 
    @Test
    fun `loadData updates state with success`() = runTest {
        // Arrange
        val testData = listOf(Item(1, "Test"))
        coEvery { mockRepository.getData() } returns Result.success(testData)
 
        // Act
        viewModel.loadData()
        advanceUntilIdle()  // Wait for coroutines
 
        // Assert
        val state = viewModel.uiState.value
        assertEquals(testData, state.items)
        assertFalse(state.isLoading)
        assertNull(state.error)
    }
}

Testing StateFlow

Collecting Multiple Emissions

@Test
fun `stateFlow emits loading then success`() = runTest {
    val emissions = mutableListOf<UiState>()
 
    val job = launch {
        viewModel.uiState.collect { emissions.add(it) }
    }
 
    viewModel.loadData()
    advanceUntilIdle()
    job.cancel()
 
    // Should have: initial, loading, success
    assertEquals(3, emissions.size)
    assertFalse(emissions[0].isLoading)  // Initial
    assertTrue(emissions[1].isLoading)   // Loading
    assertFalse(emissions[2].isLoading)  // Success
}

Testing with TurbineGood practice to limit the risk associated with a database migration. This involves testing the migration before it runs live.

When is the schema export useful?

Database builders can be configured to export the schema information into a file. While it’s possible to change the schema definition later, it’s best practice to limit the risk associated with a database migration. This involves testing the migration before it runs live.

When is the schema export useful?

Testing State Updates

@Test
fun `onItemClicked updates selected item`() {
    val item = Item(1, "Test")
 
    viewModel.onItemClicked(item)
 
    assertEquals(item, viewModel.uiState.value.selectedItem)
}

Testing Coroutines in ViewModels

@Test
fun `operation launches in viewModelScope`() = runTest {
    coEvery { mockRepository.save(any()) } returns Result.success(Unit)
 
    viewModel.saveData("test")
    advanceUntilIdle()
 
    coVerify { mockRepository.save("test") }
}

Best Practices

  1. Use runTest for coroutine testing
  2. Use advanceUntilIdle() to wait for coroutines
  3. Test state transitions (loading → success → idle)
  4. Mock repositories and services
  5. Test error handling alongside success cases

Last Updated: 2025-11-01

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