mobiai-android-testing

Android Testing

Comprehensive guide to writing and running tests in Android projects.

When to Use

• Writing unit tests for Android/Kotlin code
• Setting up test infrastructure
• Running and debugging test suites
• Choosing the right testing approach

Test Types

Type	Location	Framework	Speed	Uses Device
Unit	src/test/	JUnit + MockK	Fast	No
Integration	src/test/	JUnit + Robolectric	Medium	No (simulated)
UI / Instrumented	src/androidTest/	Espresso / Compose Testing	Slow	Yes

Unit Testing (JUnit + MockK)

Setup

// build.gradle.kts
dependencies {
    testImplementation("junit:junit:4.13.2")
    testImplementation("io.mockk:mockk:1.13.12")
    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.9.0")
    testImplementation("app.cash.turbine:turbine:1.2.0") // For Flow testing
}

File Location

Mirror the source path:

• Source: app/src/main/java/com/example/feature/MyViewModel.kt
• Test: app/src/test/java/com/example/feature/MyViewModelTest.kt

Test Structure

class MyViewModelTest {

    @get:Rule
    val mainDispatcherRule = MainDispatcherRule()

    private val repository: MyRepository = mockk()
    private lateinit var viewModel: MyViewModel

    @Before
    fun setUp() {
        viewModel = MyViewModel(repository)
    }

    @Test
    fun `loadData sets state to Success when repository returns data`() = runTest {
        // Given
        val expected = listOf(Item("1", "Test"))
        coEvery { repository.getData() } returns expected

        // When
        viewModel.loadData()

        // Then
        assertEquals(UiState.Success(expected), viewModel.state.value)
        coVerify(exactly = 1) { repository.getData() }
    }

    @Test
    fun `loadData sets state to Error when repository throws`() = runTest {
        // Given
        coEvery { repository.getData() } throws IOException("Network error")

        // When
        viewModel.loadData()

        // Then
        assertTrue(viewModel.state.value is UiState.Error)
    }
}