我正在使用一些代码,其中我需要测试由函数抛出的异常的类型(它是TypeError, ReferenceError等?)

我目前的测试框架是AVA,我可以测试它作为第二个参数t.throws方法,就像这里:

it('should throw Error with message \'UNKNOWN ERROR\' when no params were passed', (t) => {
  const error = t.throws(() => {
    throwError();
  }, TypeError);

  t.is(error.message, 'UNKNOWN ERROR');
});

我开始用Jest重写我的测试,但不知道如何轻松地做到这一点。这可能吗?


当前回答

您必须将期望的函数代码包装在另一个箭头函数中,否则错误将不会被捕获,断言将失败。

要测试的函数:

const testThrowingError = () => {
    throw new Error();
  };

测试:

describe("error function should Throw Error", () => {
  expect(() =>testThrowingError()).toThrowError();
});

资源: https://jestjs.io/docs/expect#tothrowerror

其他回答

还有一种更简单的方法对错误消息进行断言。这种方法的美妙之处在于,您不需要重新构造错误对象或获得完整的错误消息。只要您的错误包含错误消息的一部分,我们就可以假设它的类型是正确的。即

 const printOnlyString = (str) => {
   if(typeof str !== "string"){
     throw Error("I can only print strings ${typeof str) given");
   }
   else {
     console.log(str);
   } 
 }

expect(() => printOnlyString(123))。toThrow(/只能打印字符串/)

我最终为我们的test-utils库编写了一个方便的方法

/**
 *  Utility method to test for a specific error class and message in Jest
 * @param {fn, expectedErrorClass, expectedErrorMessage }
 * @example   failTest({
      fn: () => {
        return new MyObject({
          param: 'stuff'
        })
      },
      expectedErrorClass: MyError,
      expectedErrorMessage: 'stuff not yet implemented'
    })
 */
  failTest: ({ fn, expectedErrorClass, expectedErrorMessage }) => {
    try {
      fn()
      expect(true).toBeFalsy()
    } catch (err) {
      let isExpectedErr = err instanceof expectedErrorClass
      expect(isExpectedErr).toBeTruthy()
      expect(err.message).toBe(expectedErrorMessage)
    }
  }

我设法把一些答案结合起来,最后得到了这样的答案:

it('should throw', async () => {
    await expect(service.methodName('some@email.com', 'unknown')).rejects.toThrow(
      HttpException,
    );
  });

一个好方法是创建自定义错误类并模拟它们。然后你可以断言任何你想要的东西。

MessedUpError.ts

type SomeCrazyErrorObject = {
  [key: string]: unknown,
}

class MessedUpError extends Error {
  private customErrorData: SomeCrazyErrorObject = {};

  constructor(err?: string, data?: SomeCrazyErrorObject) {
    super(err || 'You messed up');

    Object.entries(data ?? {}).forEach(([Key, value]) => {
      this.customErrorData[Key] = value;
    });
    Error.captureStackTrace(this, this.constructor);
  }

  logMe() {
    console.log(this.customErrorData);
  }
}

export default MessedUpError;

messedUpError.test.ts

import MessedUpError from './MessedUpError';

jest.mock('./MessedUpError', () => jest.fn().mockImplementation((...args: any[]) => ({
  constructor: args,
  log: () => {},
})));

type MessedUpErrorContructorParams = Expand<typeof MessedUpError['prototype']>
const MessedUpErrorMock = MessedUpError as unknown as jest.Mock<MessedUpError, [MessedUpErrorContructorParams]>;

const serverErrorContructorCall = (i = 0) => ({
  message: MessedUpErrorMock.mock.calls[i][0],
  ...MessedUpErrorMock.mock.calls[i][1] || {},
});

beforeEach(() => {
  MessedUpErrorMock.mockClear();
});

test('Should throw', async () => {
  try {
    await someFunctionThatShouldThrowMessedUpError();
  } catch {} finally {
    expect(MessedUpErrorMock).toHaveBeenCalledTimes(1);
    const constructorParams = serverErrorContructorCall();
    expect(constructorParams).toHaveProperty('message', 'You messed up');
    expect(constructorParams).toHaveProperty('customErrorProperty', 'someValue');
  }
});

断言总是在finally子句中。通过这种方式,它将始终被断言。即使测试没有抛出任何错误。

我用了一个稍微简洁一点的版本:

expect(() => {
  // Code block that should throw error
}).toThrow(TypeError) // Or .toThrow('expectedErrorMessage')