javascript - How to properly make mock throw an error in Jest? - Stack Overflow

admin管理员组

文章数量:1133683

I'm testing my GraphQL api using Jest.

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

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: '[email protected]' };

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

    console.log(result);

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

    // test resolvers
  });

When I console.log(result) I get

{ data: { forgotPassword: true } }

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

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');

And it works fine, the error is thrown

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

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() {
...

UPDATE

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

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

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

I'm testing my GraphQL api using Jest.

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

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: '[email protected]' };

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

    console.log(result);

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

    // test resolvers
  });

When I console.log(result) I get

{ data: { forgotPassword: true } }

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

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');

And it works fine, the error is thrown

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

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() {
...

UPDATE

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

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

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

• javascript
• meteor
• graphql
• jestjs

Share Improve this question Follow edited Jan 28, 2019 at 22:55 dwjohnston 11.7k3939 gold badges114114 silver badges213213 bronze badges asked Apr 14, 2018 at 19:18 Le garconLe garcon 8,3471010 gold badges3333 silver badges4848 bronze badges 2

• 1 It looks like your mock is returning an error object, not throwing it. Without seeing your code that you are testing, I can only share the experience I had. I forgot to mock a function called in my mutation, which caused an error to be thrown unintentionally. Perhaps there is something similar happening for you? – Rhuarc13 Commented May 14, 2018 at 13:54
• Do you manage to make this test not log an error to the console? All my mocks which throws causes an error of "Unexpected error" to appear in the console, even with the test passing. – César Rodriguez Commented Apr 3, 2024 at 20:07

Add a comment  | 

4 Answers 4

Sorted by: Reset to default 377

Change .mockReturnValue with .mockImplementation:

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

in case you want to assert

   test('the fetch fails with an error', () => {
     return expect(fetchData()).rejects.toMatch('error');
   });

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

For promises, can use https://jestjs.io/docs/mock-function-api#mockfnmockrejectedvaluevalue

test('async test', async () => {
  const asyncMock = jest.fn().mockRejectedValue(new Error('Async error'));

  await asyncMock(); // throws "Async error"
});

For testing that error was thrown or not, can use https://eloquentcode.com/expect-a-function-to-throw-an-exception-in-jest

const func = () => {
  throw new Error('my error')
}
it('should throw an error', () => {
    expect(func).toThrow()
})

For Angular + Jest:

import { throwError } from 'rxjs';

yourMockInstance.mockImplementation(() => {
  return throwError(new Error('my error message'));
});

make sure to add throw new Error('Network error or something') either in catch block or conditionally.

import fetchApi from '../src'

it("should throw error", async () => {
    const errorMessage: string = "Network Error";
    
    (axios.post as jest.Mock).mockRejectedValueOnce(new Error(errorMessage));
    
    expect(async () => await fetchApi()).rejects.toThrow(
          errorMessage
    );
});

本文标签： javascriptHow to properly make mock throw an error in JestStack Overflow