[Vuejs]-How to stub/mock a return value with Sinon.js (vue) to test my method

Here is the unit test solution, you can use jest.mock() or jest.spyOn() to mock or spy on the apiService.getAllGroups method.

group.js:

import apiService from './apiservice';

class Group {
  groups = [];
  getAllGroups() {
    return apiService
      .getAllGroups()
      .then((data) => {
        this.groups = data;
      })
      .catch((error) => {
        console.log(error.response.data.message);
      });
  }
}

export default Group;

apiservice.js:

const apiService = {
  async getAllGroups() {
    return [];
  },
};

export default apiService;

group.test.js:

import Group from './group';
import apiService from './apiservice';

describe('59591410', () => {
  afterEach(() => {
    jest.restoreAllMocks();
  });
  it('should get all groups correctly', async () => {
    jest.spyOn(apiService, 'getAllGroups').mockResolvedValueOnce([1, 2]);
    const group = new Group();
    await group.getAllGroups();
    expect(group.groups).toEqual([1, 2]);
  });

  it('should handle error', async () => {
    const error = { response: { data: { message: 'some error' } } };
    jest.spyOn(apiService, 'getAllGroups').mockRejectedValueOnce(error);
    jest.spyOn(console, 'log');
    const group = new Group();
    await group.getAllGroups();
    expect(console.log).toBeCalledWith('some error');
  });
});

Unit test result with coverage report:

 PASS  src/stackoverflow/59591410/group.test.js
  59591410
    ✓ should get all groups correctly (10ms)
    ✓ should handle error (6ms)

  console.log node_modules/jest-mock/build/index.js:860
    some error

---------------|----------|----------|----------|----------|-------------------|
File           |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
---------------|----------|----------|----------|----------|-------------------|
All files      |    92.31 |      100 |       80 |    91.67 |                   |
 apiservice.js |    66.67 |      100 |        0 |    66.67 |                 3 |
 group.js      |      100 |      100 |      100 |      100 |                   |
---------------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        6.114s, estimated 12s

Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/59591410