android/.claude/skills/reviewing-changes/reference/testing-patterns.md

Testing Patterns Quick Reference

Quick reference for Bitwarden Android testing patterns during code reviews. For comprehensive details, read docs/ARCHITECTURE.md and docs/STYLE_AND_BEST_PRACTICES.md.

ViewModel Tests

✅ GOOD - Tests behavior:

@Test
fun `when login succeeds then state updates to success`() = runTest {
    // Arrange
    val viewModel = LoginViewModel(mockRepository)
    coEvery { mockRepository.login(any(), any()) } returns Result.success(User())

    // Act
    viewModel.onLoginClicked("user@example.com", "password")

    // Assert
    viewModel.state.test {
        assertEquals(LoginState.Loading, awaitItem())
        assertEquals(LoginState.Success, awaitItem())
    }
}

❌ BAD - Tests implementation:

@Test
fun `repository is called with correct parameters`() {
    // ❌ This tests implementation details, not behavior
    viewModel.onLoginClicked("user", "pass")
    coVerify { mockRepository.login("user", "pass") }
}

Key Rules:

• Test behavior, not implementation
• Use runTest for coroutine tests
• Use Turbine for Flow testing
• Use MockK for mocking

---

Repository Tests

✅ GOOD - Tests data transformations:

@Test
fun `fetchItems maps API response to domain model`() = runTest {
    // Arrange
    val apiResponse = listOf(ApiItem(id = "1", name = "Test"))
    coEvery { apiService.getItems() } returns apiResponse

    // Act
    val result = repository.fetchItems()

    // Assert
    assertTrue(result.isSuccess)
    assertEquals(
        listOf(DomainItem(id = "1", name = "Test")),
        result.getOrThrow()
    )
}

Key Rules:

• Test data transformations
• Test error handling (network failures, API errors)
• Test caching behavior if applicable
• Mock API services and databases

Reference: Project uses JUnit 5, MockK, Turbine, kotlinx-coroutines-test

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Null Safety

✅ GOOD - Safe handling:

// Safe call with elvis operator
val result = apiService.getData() ?: return State.Error("No data")

// Let with safe call
intent?.getStringExtra("key")?.let { value ->
    processValue(value)
}

// Require with message
val data = requireNotNull(response.data) { "Response data must not be null" }

❌ BAD - Unsafe assertions:

// ❌ Unsafe - can crash
val result = apiService.getData()!!

// ❌ Platform type unchecked
val intent: Intent = getIntent()  // Could be null from Java
val value = intent.getStringExtra("key")  // Potential NPE

Key Rules:

• Avoid !! unless safety is guaranteed (rare)
• Handle platform types with explicit nullability
• Use safe calls (?.), elvis operator (?:), or explicit checks
• Use requireNotNull with descriptive message if crash is acceptable

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Quick Checklist

Testing

• ViewModels have unit tests?
• Tests verify behavior, not implementation?
• Edge cases covered?
• Error scenarios tested?

Code Quality

• Null safety handled properly (no !! without guarantee)?
• Public APIs have KDoc?
• Following naming conventions?

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For comprehensive details, always refer to:

• docs/ARCHITECTURE.md - Full architecture patterns
• docs/STYLE_AND_BEST_PRACTICES.md - Complete style guide