如何使用Mockito测试方法中抛出的CustomException异常场景？

问题描述 #

我已通过Mockito完成了目标方法正常返回路径的测试，现需测试该方法捕获FeignException后抛出CustomException的异常场景。以下是目标方法代码及正常路径测试代码，请问该如何实现异常测试？

目标方法代码 #

@Override
public Response generateResponse(Request request) throws CustomException {           
    try {
        GenerateResponse response = client.generateResponse(headers, generateRequest);
        return response;
    } catch (FeignException.BadRequest badRequest) {
        String message = "Received Bad Request";
        throw new CustomException(message, "" + badRequest.status());
    } catch (FeignException.Unauthorized unauthorized) {
        log.error(unauthorized.contentUTF8());
        String message = "Received UnAuthorized Exception ";
        throw new CustomException(message, "" + unauthorized.status());
    } 
}

正常路径测试代码 #

Mockito.when(service.getResponse(Mockito.any(), Mockito.any())).thenReturn(getResponse);

异常场景测试实现 #

针对两种FeignException子类的捕获场景，分别编写测试代码：

1. 测试FeignException.BadRequest场景 #

通过Mockito模拟FeignClient抛出FeignException.BadRequest，验证目标方法是否抛出符合预期的CustomException：

// 模拟FeignClient抛出BadRequest异常
FeignException.BadRequest badRequestEx = FeignException.badRequest("测试BadRequest", null);
Mockito.when(client.generateResponse(Mockito.any(), Mockito.any())).thenThrow(badRequestEx);

// 调用目标方法，捕获预期的CustomException
CustomException actualEx = Assertions.assertThrows(CustomException.class, () -> {
    targetService.generateResponse(mockRequest); // mockRequest为预先构造的测试Request对象
});

// 验证异常的消息和状态码是否符合预期
Assertions.assertEquals("Received Bad Request", actualEx.getMessage());
Assertions.assertEquals("400", actualEx.getStatus()); // 假设CustomException有getStatus()方法获取状态码

2. 测试FeignException.Unauthorized场景 #

模拟FeignException.Unauthorized异常，同时验证日志是否正确输出：

// 模拟FeignClient抛出Unauthorized异常
FeignException.Unauthorized unauthorizedEx = FeignException.unauthorized("测试Unauthorized", null);
Mockito.when(client.generateResponse(Mockito.any(), Mockito.any())).thenThrow(unauthorizedEx);

// 调用目标方法，捕获CustomException
CustomException actualEx = Assertions.assertThrows(CustomException.class, () -> {
    targetService.generateResponse(mockRequest);
});

// 验证异常信息和状态码
Assertions.assertEquals("Received UnAuthorized Exception ", actualEx.getMessage());
Assertions.assertEquals("401", actualEx.getStatus());

// 验证日志是否正确打印了异常内容（需确保log对象已被Mock）
Mockito.verify(log, Mockito.times(1)).error(unauthorizedEx.contentUTF8());

注意事项 #

• 确保client和log对象已通过@Mock注解被Mockito模拟，并注入到测试的目标service中
• 使用JUnit 5的Assertions.assertThrows捕获并验证异常，若用JUnit 4则可使用ExpectedException规则或try-catch方式
• 测试前需构造好mockRequest等测试依赖对象

内容的提问来源于stack exchange，提问作者unknown1101