NullPointerException when mocking repository JUnit

Question

I have created a basic Rest API with a Controller, Service and Repository layer. I am now trying to write a unit test for the Service layer method that finds product by the product id. However, when I run the test it throws a NullPointerException in the line where I am trying to mock the repository findById() method.

The getProductById() method in the service layer is as follows:

public Product getProductById(String id){ return productRepository.findById(id).orElse(null); }

My test class for the service layer:

package com.product.Services;

import com.product.Entities.Product;
import com.product.Repositories.ProductRepository;
import org.junit.jupiter.api.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.MockitoJUnitRunner;
import static org.junit.jupiter.api.Assertions.*;
import static org.mockito.Mockito.when;

@RunWith(MockitoJUnitRunner.class)

class ProductServiceTest {

   @InjectMocks
   ProductService productService;

   @Mock
   ProductRepository productRepository;

   @Test
   void getProductById() throws Exception {

      Product product = new Product();
      product.setId("001");
      product.setName("TV");
      product.setPrice(999.99);

      when(productRepository.findById("001").orElse(null)).thenReturn(product);
      assertEquals(product,productService.getProductById("001"));
   }
}

Attaching a picture of what the debugger shows:

Answer 1

The problem is that 2 different versions of JUnit are used here: org.junit.jupiter.api.Test is from JUnit5, while org.junit.runner.RunWith is from JUnit4.

RunWith does not exist anymore in JUnit5.

In this specific case, I would use JUnit4 - ie use the annotation org.junit.Test (instead of org.junit.jupiter.api.Test ) to annotate your test.

How to use Mockito with JUnit5 provides other valid solutions.

Answer 2

JUnit 5 使用@ExtendWith(SpringExtension.class)注解，你能不能改变@RunWith注解再试一次？

Answer 3

您应该模拟findById调用，而不是与orElse链接的表达式：

when(productRepository.findById("001")).thenReturn(product);