Unit testing http methods (get, post) in react / javascript using intern

I haven't used fetch-mock before, and there are many ways to go about something like this, but the general process for mocking is to setup the mock, do what you need to do, and tear it down in an after or afterEach. How you actually go about checking whether your GET request worked depends on how you go about making the request in the first place.

A test for a mock request might look something like this. The assumption here is that you have a request method that makes a request and returns a Promise (what you'd get if you did return fetch('some_url')).

import * as fetchMock from 'fetch-mock';
const { describe, it, afterEach } = intern.getPlugin('interface.bdd');
const { expect } = intern.getPlugin('chai');

describe('my suite', () => {
  afterEach(() => {
    fetchMock.restore();
  });

  it('should do something', () => {
    fetchMock.get('*', { hello: 'world' });
    return thingThatDoesAGetRequest.then(response => {
      expect(response).to.equal({ hello: 'world' });
    });
  })
});

Another option would be to wait for the mock request to complete rather than looking at a function return value:

it('should do something', test => {
  // Create a promise that will resolve when a request is made
  const promise = new Promise(resolve => {
    fetchMock.get('*', () => {
      resolve();
      return { hello: 'world' }
    });
  });

  // Do whatever should be making a call
  thingThatDoesAGetRequest();

  // Wait for the request promise to resolve, then see if whatever
  // you expect to happen has happened
  return promise.then(() => {
    expect(something).to.equal({ hello: 'world' });
  });
})