如何正确地使模拟在 Jest 中抛出错误? [英] How to properly make mock throw an error in Jest?

问题描述

我正在使用 Jest 测试我的 GraphQL api.

I'm testing my GraphQL api using Jest.

我为每个查询/变异使用单独的测试套装

I'm using a separate test suit for each query/mutation

我有 2 个测试(每个测试都在单独的测试套件中)，其中我模拟了一个用于突变的函数(即 Meteor 的 callMethod).

I have 2 tests (each one in a separate test suit) where I mock one function (namely, Meteor's callMethod) that is used in mutations.

  it('should throw error if email not found', async () => {
    callMethod
      .mockReturnValue(new Error('User not found [403]'))
      .mockName('callMethod');

    const query = FORGOT_PASSWORD_MUTATION;
    const params = { email: '[e-mail]' };

    const result = await simulateQuery({ query, params });

    console.log(result);

    // test logic
    expect(callMethod).toBeCalledWith({}, 'forgotPassword', {
      email: '[e-mail]',
    });

    // test resolvers
  });

当我 console.log(result) 我得到

When I console.log(result) I get

{ data: { forgotPassword: true } }

这种行为不是我想要的，因为在 .mockReturnValue 中我抛出了一个错误，因此期望 result 有一个错误对象

This behaviour is not what I want because in .mockReturnValue I throw an Error and therefore expect result to have an error object

然而，在这个测试之前，运行了另一个

Before this test, however, another is ran

 it('should throw an error if wrong credentials were provided', async () => {
    callMethod
      .mockReturnValue(new Error('cannot login'))
      .mockName('callMethod');

它工作正常，错误被抛出

And it works fine, the error is thrown

我想问题在于测试完成后模拟不会重置.在我的 jest.conf.js 我有 clearMocks: true

I guess the problem is that mock doesn't get reset after the test finishes. In my jest.conf.js I have clearMocks: true

每个测试套件都在一个单独的文件中，我在测试之前模拟函数，如下所示:

Each test suit is in a separate file, and I mock functions before tests like this:

import simulateQuery from '../../../helpers/simulate-query';

import callMethod from '../../../../imports/api/users/functions/auth/helpers/call-accounts-method';

import LOGIN_WITH_PASSWORD_MUTATION from './mutations/login-with-password';

jest.mock(
  '../../../../imports/api/users/functions/auth/helpers/call-accounts-method'
);

describe('loginWithPassword mutation', function() {
...

更新

当我用 .mockImplementation 替换 .mockReturnValue 时，一切都按预期进行:

When I substituted .mockReturnValue with .mockImplementation everything worked out as expected:

callMethod.mockImplementation(() => {
  throw new Error('User not found');
});

但这并不能解释为什么在另一个测试中 .mockReturnValue 工作正常...

But that doesn't explain why in another test .mockReturnValue works fine...

推荐答案

Change .mockReturnValue with .mockImplementation:

Change .mockReturnValue with .mockImplementation:

yourMockInstance.mockImplementation(() => {
  throw new Error();
});

如果这是一个承诺，你也可以 .rejects www.jestjs.io/docs/en/asynchronous#resolves--rejects

If it's a promise you can also to .rejects www.jestjs.io/docs/en/asynchronous#resolves--rejects

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