Tests unitaires

On utilise souvent la matrice Given-When-Then :

@ExtendWith(MockitoExtension::class)
class ProductServiceTest {

    @Mock
    private lateinit var productRepository: ProductRepository
    
    @Mock
    private lateinit var categoryRepository: CategoryRepository
    
    @InjectMocks
    private lateinit var productService: ProductService

    @Test
    @DisplayName("Should create product successfully when category exists")
    fun `should create product when category exists`() {
        // Given
        val categoryId = UUID.fromString("550e8400-e29b-41d4-a716-446655440010")
        val productId = UUID.fromString("550e8400-e29b-41d4-a716-446655440020")
        
        val createDTO = CreateProductDTO(
            name = "iPhone 15",
            description = "Latest Apple smartphone",
            price = BigDecimal("1199.99"),
            stock = 50,
            categoryId = categoryId
        )
        
        val category = Category(categoryId, "Smartphones", "Mobile devices")
        val savedProduct = Product(productId, "iPhone 15", "Latest Apple smartphone", 
            BigDecimal("1199.99"), 50, category, ProductStatus.ACTIVE)
        
        `when`(categoryRepository.findById(categoryId)).thenReturn(Optional.of(category))
        `when`(productRepository.save(any(Product::class.java))).thenReturn(savedProduct)

        // When
        val result = productService.createProduct(createDTO)

        // Then
        assertThat(result).isNotNull
        assertThat(result.id).isEqualTo(productId)
        assertThat(result.name).isEqualTo("iPhone 15")
        assertThat(result.price).isEqualByComparingTo(BigDecimal("1199.99"))
        assertThat(result.stock).isEqualTo(50)
        
        verify(categoryRepository).findById(categoryId)
        verify(productRepository).save(any(Product::class.java))
    }

    @Test
    @DisplayName("Should throw exception when category not found")
    fun `should throw exception when category not found`() {
        // Given
        val categoryId = UUID.fromString("550e8400-e29b-41d4-a716-446655440099")
        val createDTO = CreateProductDTO("iPhone 15", "Description", BigDecimal("1199.99"), 50, categoryId)
        
        `when`(categoryRepository.findById(categoryId)).thenReturn(Optional.empty())

        // When & Then
        assertThatThrownBy { productService.createProduct(createDTO) }
            .isInstanceOf(CategoryNotFoundException::class.java)
            .hasMessageContaining(categoryId.toString())
        
        verify(categoryRepository).findById(categoryId)
        verifyNoInteractions(productRepository)
    }
}