Quarkus TDD Workflow

TDD guidance for Quarkus 3.x services with 80%+ coverage (unit + integration). Optimized for event-driven architectures with Apache Camel.

When to Use

• New features or REST endpoints
• Bug fixes or refactors
• Adding data access logic, security rules, or reactive streams
• Testing Apache Camel routes and event handlers
• Testing event-driven services with RabbitMQ
• Testing conditional flow logic
• Validating CompletableFuture async operations
• Testing LogContext propagation

Workflow

1. Write tests first (they should fail)
2. Implement minimal code to pass
3. Refactor with tests green
4. Enforce coverage with JaCoCo (80%+ target)

Unit Tests with @Nested Organization

Follow this structured approach for comprehensive, readable tests:

@ExtendWith(MockitoExtension.class)
@DisplayName("OrderService Unit Tests")
class OrderServiceTest {

  @Mock
  private OrderRepository orderRepository;

  @Mock
  private EventService eventService;

  @Mock
  private FulfillmentPublisher fulfillmentPublisher;

  @InjectMocks
  private OrderService orderService;

  private CreateOrderCommand validCommand;

  @BeforeEach
  void setUp() {
    validCommand = new CreateOrderCommand(
        "customer-123",
        List.of(new OrderLine("sku-123", 2))
    );
  }

  @Nested
  @DisplayName("Tests for createOrder")
  class CreateOrder {

    @Test
    @DisplayName("Should persist order and publish fulfillment event")
    void givenValidCommand_whenCreateOrder_thenPersistsAndPublishes() {
      // ARRANGE
      doNothing().when(orderRepository).persist(any(Order.class));

      // ACT
      OrderReceipt receipt = orderService.createOrder(validCommand);

      // ASSERT
      assertThat(receipt).isNotNull();
      assertThat(receipt.customerId()).isEqualTo("customer-123");
      verify(orderRepository).persist(any(Order.class));
      verify(fulfillmentPublisher).publishAsync(receipt);
      verify(eventService).createSuccessEvent(receipt, "ORDER_CREATED");
    }

    @Test
    @DisplayName("Should reject missing customer id")
    void givenMissingCustomerId_whenCreateOrder_thenThrowsBadRequest() {
      // ARRANGE
      CreateOrderCommand invalid = new CreateOrderCommand("", validCommand.lines());

      // ACT & ASSERT
      WebApplicationException exception = assertThrows(
          WebApplicationException.class,
          () -> orderService.createOrder(invalid)
      );

      assertThat(exception.getResponse().getStatus()).isEqualTo(400);
      verify(orderRepository, never()).persist(any(Order.class));
      verify(fulfillmentPublisher, never()).publishAsync(any());
    }

    @Test
    @DisplayName("Should record error event when persistence fails")
    void givenPersistenceFailure_whenCreateOrder_thenRecordsErrorEvent() {
      // ARRANGE
      doThrow(new PersistenceException("database unavailable"))
          .when(orderRepository).persist(any(Order.class));

      // ACT & ASSERT
      PersistenceException exception = assertThrows(
          PersistenceException.class,
          () -> orderService.createOrder(validCommand)
      );

      assertThat(exception.getMessage()).contains("database unavailable");
      verify(eventService).createErrorEvent(
          eq(validCommand),
          eq("ORDER_CREATE_FAILED"),
          contains("database unavailable")
      );
      verify(fulfillmentPublisher, never()).publishAsync(any());
    }

    @Test
    @DisplayName("Should reject null commands")
    void givenNullCommand_whenCreateOrder_thenThrowsNullPointerException() {
      // ACT & ASSERT
      assertThrows(
          NullPointerException.class,
          () -> orderService.createOrder(null)
      );

      verify(orderRepository, never()).persist(any(Order.class));
    }
  }
}

Key Testing Patterns

1. @Nested Classes: Group tests by method being tested
2. @DisplayName: Provide readable test descriptions for test reports
3. Naming Convention: givenX_whenY_thenZ for clarity
4. AAA Pattern: Explicit // ARRANGE, // ACT, // ASSERT comments
5. @BeforeEach: Setup common test data to reduce duplication
6. assertDoesNotThrow: Test success scenarios without catching exceptions
7. assertThrows: Test exception scenarios with message validation using AssertJ
8. Comprehensive Coverage: Test happy paths, null inputs, edge cases, exceptions
9. Verify Interactions: Use Mockito verify() to ensure methods are called correctly

…