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Testing Strategy

Comprehensive testing approach for quality assurance.

Test Pyramid

       ┌─────────────┐
       │   E2E Tests │  (Few, slow, high confidence)
       └─────────────┘
      ┌───────────────┐
      │ Integration   │  (Some, medium speed)
      │     Tests     │
      └───────────────┘
   ┌──────────────────────┐
   │    Unit Tests        │  (Many, fast, focused)
   └──────────────────────┘

Android Testing

Unit Tests

Location: app/src/test/java/

Example:

class PaymentCalculatorTest {
    @Test
    fun `calculates correct payment date`() {
        val card = CreditCard(
            statementGenerationDay = 18,
            institution = BankInstitution.CHASE,
            currentBalance = 1500.0
        )
        
        val recommendation = PaymentCalculator.calculateRecommendation(card)
        
        assertEquals(LocalDate.of(2025, 10, 15), recommendation.recommendedPaymentDate)
        assertEquals(1500.0, recommendation.recommendedAmount)
    }
}

Run:

./gradlew test
./gradlew test --tests PaymentCalculatorTest

Instrumented Tests

Location: app/src/androidTest/java/

Example:

@RunWith(AndroidJUnit4::class)
class MainActivityTest {
    @get:Rule
    val composeTestRule = createComposeRule()
    
    @Test
    fun testMainScreen() {
        composeTestRule.setContent {
            CreditCardOptimizerTheme {
                MainScreen(viewModel)
            }
        }
        
        composeTestRule.onNodeWithText("Connect with Plaid").assertExists()
    }
}

Run:

./gradlew connectedAndroidTest

Backend Testing

Unit Tests

Location: backend/src/__tests__/

Example:

describe('AuthService', () => {
    it('should register user', async () => {
        const result = await authService.register(
            'test@example.com',
            'TestPass123'
        );
        
        expect(result.user.email).toBe('test@example.com');
        expect(result.token).toBeDefined();
    });
    
    it('should reject weak password', async () => {
        await expect(
            authService.register('test@example.com', 'weak')
        ).rejects.toThrow();
    });
});

Run:

npm test
npm test -- --coverage

Coverage Requirements

Minimum: 95%

npm run coverage

# Should show:
# Statements: 95%+
# Branches: 95%+
# Functions: 95%+
# Lines: 95%+

Enforce in CI:

npm run coverage -- --coverageThreshold='{"global":{"lines":95}}'

Test Data

Plaid Sandbox

Test credentials:

  • Username: user_good
  • Password: pass_good
  • MFA code: 1234

Test accounts:

  • Chase: Credit card with $10,000 limit
  • Bank of America: Credit card with $15,000 limit

Mock Data

object TestData {
    val mockCreditCard = CreditCard(
        id = "test-123",
        name = "Test Card",
        statementGenerationDay = 18,
        currentBalance = 1500.0
    )
    
    val mockRecommendation = PaymentRecommendation(
        creditCard = mockCreditCard,
        recommendedPaymentDate = LocalDate.now().plusDays(5)
    )
}

Mocking

Android

@Test
fun testRepository() {
    val mockApi = mock<PlaidApi>()
    val repository = PlaidRepository(mockApi)
    
    whenever(mockApi.getAccounts()).thenReturn(listOf(mockAccount))
    
    val result = runBlocking { repository.getAccounts() }
    assertEquals(1, result.getOrNull()?.size)
}

Backend

jest.mock('../repositories/userRepository');

test('should call repository', async () => {
    userRepository.findByEmail.mockResolvedValue(mockUser);
    
    const user = await authService.login('test@example.com', 'password');
    expect(userRepository.findByEmail).toHaveBeenCalled();
});

Best Practices

  1. Test Naming: Use descriptive names

    fun `should reject payment for card without statement date`()

  2. Arrange-Act-Assert:

    // Arrange
val card = createTestCard()

// Act
val result = calculate(card)

// Assert
assertEquals(expected, result)

  3. Test One Thing: Each test should test one behavior

  4. Mock External Dependencies: Don't rely on actual APIs

  5. Clean Up: Reset state after each test

CI/CD Integration

# GitHub Actions example
- name: Run Android Tests
  run: ./gradlew test

- name: Run Backend Tests
  run: cd backend && npm test

- name: Check Coverage
  run: cd backend && npm run coverage

See Also: