sinon-ajax-mocker.js

class Ajax {
  static respondTo(request, resHash, code = 200) {
    request.respond(code,
                    { 'Content-Type': 'application/json' },
                    JSON.stringify(resHash));
  }

  constructor() {
    this._ajax = sinon.useFakeXMLHttpRequest();
    let requests = this.requests = [];
    this._ajax.onCreate = function(xhr) {
      requests.push(xhr);
    };
  }

  get firstRequest() {
    return this.requests[0];
  }

  restore() {
    this._ajax.restore();
  }

  respond(resHash, code = 200) {
    return Ajax.respondTo(this.firstRequest, resHash, code);
  }
}

function ensureRequestWith ({ url, method = 'GET', body, execute }) {
  describe(`Request to ${url}`, function(){
    let ajax;
    let data = { key: 'val' };
    beforeEach(function(){
      ajax = new Ajax();
    });
    afterEach(function(){
      ajax.restore();
    });
    it('sends request to server', function(){
      let request;

      execute();
      request = ajax.firstRequest;

      expect(request.url).to.equal(url);
      expect(request.method).to.equal(method);
      if ( body ) {
        expect(request.requestBody).to.deep.equal(JSON.stringify(body));
      }
    });
    it('resolves returned promise', function(){
      let promise = execute();

      ajax.respond(data);

      return expect(promise).to.eventually.deep.equal(data);
    });
    it('reject returned promise when failed', function(){
      let promise = execute();

      ajax.respond(data, 409);

      return expect(promise).to.be.rejected;
    });
  });
}

let stubApiUtil = function(apiUtil, methodName) {
  let deferred = Promise.defer();
  sinon.stub(apiUtil, methodName);
  apiUtil[methodName].returns(deferred.promise);
  return deferred;
}

export default Ajax;
export { Ajax as AjaxMocker };
export { ensureRequestWith };
export { stubApiUtil };