mock-axios-setup.test.js

import MockAdapter from 'axios-mock-adapter';
import apiClient from 'helpers/api-client';
import { userObject } from 'jest/mockResponseObjects/user-objects';

const mockApi = new MockAdapter(apiClient.getAxiosInstance());
const validAuth = '{"email":"email@test.com","password":"password"}';

mockApi.onPost('sessions').reply((config) => {
  if (config.data === validAuth) {
    return [200, userObject];
  }
  return [400, 'Bad Credentials'];
});