Should a plugin be trusted to write unit tests?

Question

Java

While studying testing, I came across a plugin

Diff blue

who writes the tests.
In testing, I don’t understand anything yet to evaluate the result. Please evaluate the work
result of the plugin.

Normal service class:

@Service
@Slf4j
public class ProductService {

  @Autowired
  private   ProductRepository repo;

  public List<Product> listAll(String keyword) {
    if (keyword != null) {
      log.info("Поиск продукта по ключевому слову {}", keyword);
      return repo.search(keyword);
    }
    return repo.findAll();
  }
  
  public void save(Product product) {
    if (product != null){
      repo.save(product);
    }else {
      log.error("Продукт не может быть пустым!");
    }
  }
  
  public Product get(Long id) {
    if (repo.findById(id).isPresent()){
      return repo.findById(id).get();
    }
    log.error("Продукт не найден");
    return null;
  }
  
  public void delete(Long id) {
    log.warn("Продукт по id {} удален", id);
    repo.deleteById(id);
  }

  public List<Product> getAll(){
    return repo.findAll();
  }

}

test:

@ContextConfiguration(classes = {ProductService.class})
@ExtendWith(SpringExtension.class)
class ProductServiceTest {
    @MockBean
    private ProductRepository productRepository;

    @Autowired
    private ProductService productService;

    @Test
    void testListAll() {
        ArrayList<Product> productList = new ArrayList<Product>();
        when(this.productRepository.search((String) any())).thenReturn(productList);
        List<Product> actualListAllResult = this.productService.listAll("Keyword");
        assertSame(productList, actualListAllResult);
        assertTrue(actualListAllResult.isEmpty());
        verify(this.productRepository).search((String) any());
        assertTrue(this.productService.getAll().isEmpty());
    }



    @Test
    void testSave() {
        Product product = new Product();
        product.setPrice(10.0);
        product.setId(123L);
        product.setName("Name");
        product.setCategoryList(new ArrayList<Category>());
        product.setDescription("The characteristics of someone or something");
        product.setCategory2("Category2");
        when(this.productRepository.save((Product) any())).thenReturn(product);

        Product product1 = new Product();
        product1.setPrice(10.0);
        product1.setId(123L);
        product1.setName("Name");
        product1.setCategoryList(new ArrayList<Category>());
        product1.setDescription("The characteristics of someone or something");
        product1.setCategory2("Category2");
        this.productService.save(product1);
        verify(this.productRepository).save((Product) any());
        assertTrue(this.productService.getAll().isEmpty());
    }


    @Test
    void testGet() {
        Product product = new Product();
        product.setPrice(10.0);
        product.setId(123L);
        product.setName("Name");
        product.setCategoryList(new ArrayList<Category>());
        product.setDescription("The characteristics of someone or something");
        product.setCategory2("Category2");
        Optional<Product> ofResult = Optional.<Product>of(product);
        when(this.productRepository.findById((Long) any())).thenReturn(ofResult);
        assertSame(product, this.productService.get(123L));
        verify(this.productRepository, atLeast(1)).findById((Long) any());
        assertTrue(this.productService.getAll().isEmpty());
    }



    @Test
    void testDelete() {
        doNothing().when(this.productRepository).deleteById((Long) any());
        this.productService.delete(123L);
        verify(this.productRepository).deleteById((Long) any());
        assertTrue(this.productService.getAll().isEmpty());
    }



    @Test
    void testGetAll() {
        ArrayList<Product> productList = new ArrayList<Product>();
        when(this.productRepository.findAll()).thenReturn(productList);
        List<Product> actualAll = this.productService.getAll();
        assertSame(productList, actualAll);
        assertTrue(actualAll.isEmpty());
        verify(this.productRepository).findAll();
    }

}

Answer 1

It is worth adhering to the rule not to trust more than one automatic tool until you understand how it works under the hood and what tests it generates. In this case, the generation of tests itself is a useless exercise, since you don’t even know what exactly this code is testing and how.

Answer 2

I don't think it makes sense, since the essence of the test is to check the correctness of the code. These tests are generated so that they pass with the current code. So they are only suitable as protection against changes in behavior during refactoring