How to mock jest.spyOn for a specific axios call

Question

How do I mock a specific axios call? Imagine 2 GET calls:

await axios.get('api/numbers');
await axios.get('api/letters');

Then this is going on in the test:

const mockGet = jest.spyOn(axios, 'get');
mockGet.mockReturnValueOnce(Promise.resolve({ data: 1 }));
mockGet.mockReturnValueOnce(Promise.resolve({ data: 'a' }));

How do I create a condition for mockReturnValueOnce based on the url passed to axios (say for 'api/numbers' -> return Promise.resolve({ data: 1 }))

Answer 1

So far, there is no method of jestjs to do this. Here is the proposal: Parameterised mock return values

Here are the solutions:

1. Use sinon.js

sinon.js support mock the returned value based on the arguments, there is a method named stub.withArgs(arg1[, arg2, ...]);

2. Use jest-when - A when(fn).calledWith(args).thenReturn(value) lib for jest

3. If you insist on using jestjs, since mockReturnValueOnce returns values sequentially(first call, second call, etc.). You can use the below way:

index.js:

import axios from 'axios';

export async function main() {
  const numbersRes = await axios.get('api/numbers');
  const lettersRes = await axios.get('api/letters');
  return { numbersRes, lettersRes };
}

index.test.js:

import { main } from '.';
import axios from 'axios';

describe('59751925', () => {
  it('should pass', async () => {
    const mockGet = jest.spyOn(axios, 'get');
    mockGet.mockImplementation((url) => {
      switch (url) {
        case 'api/numbers':
          return Promise.resolve({ data: 1 });
        case 'api/letters':
          return Promise.resolve({ data: 'a' });
      }
    });
    const actual = await main();
    expect(actual.numbersRes).toEqual({ data: 1 });
    expect(actual.lettersRes).toEqual({ data: 'a' });
  });
});

Unit test results:

 PASS  src/stackoverflow/59751925/index.test.js (11.168s)
  59751925
    ✓ should pass (9ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        13.098s