In the ProductControllerTest class annotated with @SpringBootTest, we’re testing the ProductController. To isolate the controller for testing and assume that the ProductService functions correctly, we create a real instance of ProductController and a mock instance of ProductService.

Using the @MockBean annotation from Mockito framework, we mock the ProductService by defining its behavior. We specify that when the getAllProducts() method is called on the mocked productService, it should return a predefined list of products.

Next, we create three empty Product objects and add them to a list called products using Arrays.asList(). Then, we call the getAllProducts() method on the real ProductController instance, storing the result in a list named actual.

To verify that the controller returns the expected number of products, we use Assertions.assertTrue() to assert that the size of the actual list is equal to 3.

@SpringBootTest
class ProductControllerTest {
@Autowired
ProductController productController;
@MockBean
ProductService productService;
@Test
void getAllProducts() {
Product p1 = new Product();
Product p2 = new Product();
Product p3 = new Product();
List<Product> products = Arrays.asList(p1,p2,p3);
Mockito.when(productService.getAllProducts()).thenReturn(products);
List<Product> actual = productController.getAllProducts();
Assertions.assertTrue(actual.size() == 3);
}
}

Another useful scenario is to modify the logic of the getAllProducts method in the ProductController. Instead of fetching all products directly, we’ll use filtering with Java streams. This approach allows us to perform a more focused test, as we’re testing a specific functionality rather than retrieving all products. By filtering the results based on certain criteria and then testing them, we gain clearer insights into how the application behaves under specific conditions.

ProductController.java
@GetMapping(“/products”)
public List<Product> getAllProducts(){
return
productService.getAllProducts().stream().filter((product)->product.getName().startsWith(“A”)).collect(Collectors.toList());
}

ProductControllerTest.java

@SpringBootTest
class ProductControllerTest {
@Autowired
ProductController productController;
@MockBean
ProductService productService;
@Test
void getAllProducts() {
Product p1 = new Product();
p1.setName(Appo);
Product p2 = new Product();
p2.setName(Appo v1);
Product p3 = new Product();
p3.setName(iPhone);
List<Product> products = Arrays.asList(p1,p2,p3);
Mockito.when(productService.getAllProducts()).thenReturn(products);
List<Product> actual = productController.getAllProducts();
Assertions.assertTrue(actual.size() == 3);
}}