CODEWITHSUNDEEP
javascriptjestjs
dc-mpo
dc-mpo

Reputation: 393

How to mock a callback

I would like to test my function which has a callback at the end like this :

const authorizer = (event, context, callback) => {

    const token = event.authorizationToken;
    try {
        {...}
        callback(null, policyDocument)
    } catch (e) {
        callback('Unauthorized');
    }

};

But when i try to test it with jest, it return "callback is not a function". So i would like to know how to mock the callback at the end and how to call it in my jest file.

PS : my authorizer test part looks like this :

describe('authorizer', () => {
    let mockCallback, var1, var2, var3, event;

    beforeEach(async() => {
        mockCallback = jest.fn().mockReturnValue('ok')
        var 1 ='...'
        var 2 ='...'
        var 3 ='...'
        event = '...'
        actualValue = await authorize.authorizer(event, null, mockCallback)
    })

    it('should authorize', async () => {
        expect(actualValue).toHaveBeenCalled()
    })
})

response : 

Matcher error: received value must be a mock or spy function

    Received has value: undefined

Upvotes: 0

Views: 1196

Answers (1)

Lin Du
Lin Du

Reputation: 102207

Here is the solution:

index.ts:

export const authorizer = (event, context, callback) => {
  const token = event.authorizationToken;
  const policyDocument = {};
  try {
    callback(null, policyDocument);
  } catch (e) {
    callback('Unauthorized');
  }
};

index.spec.ts:

import { authorizer } from './';

describe('authorizer', () => {
  it('should authorize', () => {
    const event = 'message';
    const mockCallback = jest.fn().mockReturnValue('ok');
    authorizer(event, null, mockCallback);
    expect(mockCallback).toHaveBeenCalled();
  });
});

Unit test result with coverage report:

 PASS  src/stackoverflow/59371450/index.spec.ts (10.989s)
  authorizer
    ✓ should authorize (5ms)

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |    83.33 |      100 |      100 |    83.33 |                   |
 index.ts |    83.33 |      100 |      100 |    83.33 |                 7 |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        12.907s

Upvotes: 1

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