Testing Fundamentals

Testing Pyramid

        /\
       /  \      E2E Tests (Few, Slow, Expensive)
      /----\
     /      \    Integration Tests (Some)
    /--------\
   /          \  Unit Tests (Many, Fast, Cheap)
  /------------\

Unit Tests (70%)

• Test individual functions/methods
• Fast execution (< 100ms each)
• No external dependencies (mocked)
• High coverage of business logic

Integration Tests (20%)

• Test component interactions
• Database, API, message queue integration
• Slower but realistic
• Focus on boundaries

E2E Tests (10%)

• Test complete user flows
• Browser/API level
• Slowest, most expensive
• Critical paths only

Test Structure (AAA Pattern)

@Test
void shouldCalculateTotalWithDiscount() {
    // Arrange - Set up test data
    Order order = new Order();
    order.addItem(new Item("SKU-1", 100.00));
    order.setDiscountPercent(10);

    // Act - Execute the code
    double total = order.calculateTotal();

    // Assert - Verify results
    assertThat(total).isEqualTo(90.00);
}

Naming Conventions

// Pattern: should_[expectedBehavior]_when_[condition]
void shouldReturnEmptyList_whenNoOrdersExist() { }
void shouldThrowException_whenOrderIdIsNull() { }
void shouldCalculateCorrectTotal_whenDiscountApplied() { }

Mocking Patterns

Mock External Dependencies

@Mock
private OrderRepository orderRepository;

@Mock
private PaymentService paymentService;

@InjectMocks
private OrderService orderService;

@Test
void shouldProcessOrder() {
    when(orderRepository.findById(1L))
        .thenReturn(Optional.of(testOrder));
    when(paymentService.charge(any()))
        .thenReturn(PaymentResult.success());

    orderService.processOrder(1L);

    verify(paymentService).charge(any());
}

Don't Mock What You Own

• Mock external services (payment, email)
• Don't mock your own domain objects
• Don't mock simple value objects

Test Data Patterns

Builder Pattern

Order testOrder = OrderBuilder.anOrder()
    .withId(1L)
    .withStatus(OrderStatus.PENDING)
    .withItems(List.of(testItem))
    .build();

Test Fixtures

@BeforeEach
void setUp() {
    testCustomer = CustomerFixtures.aValidCustomer();
    testOrder = OrderFixtures.aPendingOrder(testCustomer);
}

Coverage Guidelines

What to Cover

• Business logic (always)
• Edge cases (null, empty, boundary)
• Error paths (exceptions, failures)
• State transitions

What Not to Cover

• Getters/setters (unless logic)
• Framework code
• Generated code
• Configuration classes

Testing Async Code

@Test
void shouldProcessAsync() {
    CompletableFuture<Result> future = service.processAsync(input);

    Result result = future.get(5, TimeUnit.SECONDS);

    assertThat(result.isSuccess()).isTrue();
}

Testing Temporal Workflows

@Test
void shouldCompleteWorkflow() {
    WorkflowClient client = testEnvironment.getWorkflowClient();
    MyWorkflow workflow = client.newWorkflowStub(MyWorkflow.class);

    workflow.execute(input);

    assertThat(workflow.getState()).isEqualTo(WorkflowState.COMPLETED);
}