Java单元测试实践 Java如何使用JUnit进行高效测试

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-api</artifactId>
    <version>5.10.0</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-engine</artifactId>
    <version>5.10.0</version>
    <scope>test</scope>
</dependency>

public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }

    public int divide(int a, int b) {
        if (b == 0) {
            throw new IllegalArgumentException("Divisor cannot be zero");
        }
        return a / b;
    }
}

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

class CalculatorTest {

    private Calculator calculator;

    @BeforeEach // 每个测试方法执行前都会运行
    void setUp() {
        calculator = new Calculator();
    }

    @Test // 这是一个测试方法
    void testAdd() {
        // Arrange (准备)
        int num1 = 5;
        int num2 = 3;

        // Act (执行)
        int result = calculator.add(num1, num2);

        // Assert (断言)
        assertEquals(8, result, "5 + 3 应该等于 8");
    }

    @Test
    void testDividePositiveNumbers() {
        int result = calculator.divide(10, 2);
        assertEquals(5, result);
    }

    @Test
    void testDivideByZeroThrowsException() {
        // 预期会抛出 IllegalArgumentException
        assertThrows(IllegalArgumentException.class, () -> {
            calculator.divide(10, 0);
        }, "除以零应该抛出 IllegalArgumentException");
    }

    // 还可以有更多的测试方法...
}

@Service
public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User getUserById(Long id) {
        return userRepository.findById(id).orElse(null);
    }
}

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

import java.util.Optional;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.when;

class UserServiceTest {

    @Mock // 模拟UserRepository
    private UserRepository userRepository;

    @InjectMocks // 将模拟的userRepository注入到userService中
    private UserService userService;

    @BeforeEach
    void setUp() {
        // 初始化Mockito注解
        MockitoAnnotations.openMocks(this);
    }

    @Test
    void testGetUserByIdFound() {
        Long userId = 1L;
        User mockUser = new User(userId, "Test User");

        // 当调用userRepository.findById(userId)时，返回mockUser
        when(userRepository.findById(userId)).thenReturn(Optional.of(mockUser));

        User result = userService.getUserById(userId);
        assertEquals(mockUser, result);
    }

    @Test
    void testGetUserByIdNotFound() {
        Long userId = 2L;

        // 当调用userRepository.findById(userId)时，返回Optional.empty()
        when(userRepository.findById(userId)).thenReturn(Optional.empty());

        User result = userService.getUserById(userId);
        assertEquals(null, result);
    }
}