ProductControllerTest.java

@ExtendWith(SpringExtension.class)
class ProductControllerTest {

    @InjectMocks
    private ProductController productController;

    @Mock
    private ProductService productService;

    private MockMvc mockMvc;

    private final ObjectMapper objectMapper = new ObjectMapper();

    @BeforeEach
    public void setup() {
        mockMvc = MockMvcBuilders.standaloneSetup(productController).build();

    }

    @Test
    public void it_should_test_when_product_id_is_valid() throws Exception {
        //given
        ProductRequest productRequest = ProductRequest.builder().id(1).build();
        ArgumentCaptor<ProductRequest> argumentCaptor = ArgumentCaptor.forClass(ProductRequest.class);

        //when
        ResultActions result = mockMvc.perform(post("/products")
                .content(objectMapper.writeValueAsString(productRequest))
                .contentType(MediaType.APPLICATION_JSON));

        //then
        verify(productService).dispense(argumentCaptor.capture());
        result.andExpect(status().isOk());
    }

    @Test
    public void it_should_test_when_product_id_is_not_valid() throws Exception {
        //given
        ProductRequest productRequest = ProductRequest.builder().id(0).build();

        //when
        ResultActions result = mockMvc.perform(post("/products")
                .content(objectMapper.writeValueAsString(productRequest))
                .contentType(MediaType.APPLICATION_JSON));

        //then
        verifyNoInteractions(productService);
        result.andExpect(status().isBadRequest());
    }

    @Test
    public void it_should_test_when_product_id_is_null() throws Exception {
        //given
        ProductRequest productRequest = ProductRequest.builder().build();

        //when
        ResultActions result = mockMvc.perform(post("/products")
                .content(objectMapper.writeValueAsString(productRequest))
                .contentType(MediaType.APPLICATION_JSON));

        //then
        verifyNoInteractions(productService);
        result.andExpect(status().isBadRequest());
    }
}