testing-patterns

Testing Patterns Skill

Testing strategies for Spring Boot applications. Always write both positive and negative test cases.

When to Use

• "write tests" / "add test coverage" / "test this"
• Test failures or debugging test issues
• Choosing between unit, slice, and integration tests

Test Pyramid

Unit Tests (Service Layer)

@ExtendWith(MockitoExtension.class)
class OrderServiceTest {

    @Mock
    private OrderRepository orderRepository;

    @Mock
    private ProductService productService;

    @InjectMocks
    private OrderService orderService;

    // ✅ Positive test
    @Test
    @DisplayName("Should create order with valid items")
    void shouldCreateOrder() {
        // Given
        var request = new OrderRequest(List.of(
            new OrderItem(1L, 2)
        ));
        var product = new Product();
        product.setId(1L);
        product.setPrice(new BigDecimal("10.00"));

        when(productService.findById(1L)).thenReturn(product);
        when(orderRepository.save(any(Order.class))).thenAnswer(inv -> {
            Order o = inv.getArgument(0);
            o.setId(1L);
            return o;
        });

        // When
        Order result = orderService.create(request);

        // Then
        assertThat(result.getId()).isEqualTo(1L);
        verify(orderRepository).save(any(Order.class));
    }

    // ✅ Negative test
    @Test
    @DisplayName("Should throw when product not found")
    void shouldThrowWhenProductNotFound() {
        // Given
        var request = new OrderRequest(List.of(
            new OrderItem(999L, 1)
        ));
        when(productService.findById(999L))
            .thenThrow(new EntityNotFoundException("Product not found"));

        // When & Then
        assertThatThrownBy(() -> orderService.create(request))
            .isInstanceOf(EntityNotFoundException.class)
            .hasMessageContaining("Product not found");

        verify(orderRepository, never()).save(any());
    }

    // ✅ Negative test - empty input
    @Test
    @DisplayName("Should throw when order has no items")
    void shouldThrowWhenNoItems() {
        var request = new OrderRequest(List.of());

        assertThatThrownBy(() -> orderService.create(request))
            .isInstanceOf(IllegalArgumentException.class);
    }
}