class App extends Component {
  constructor(props) {
    super(props);
    this.state = { file: 'unknown' };
  }

  queryServer = async() => {
    const that = this;
    return fetch('/api/foo')
        .then(function (response) {
            return response.json();
        })
        .then(function (json) {
            that.setState(() => { return {'file': 'api.js'}; });
        });
  };

  render() {
    return (
        <div>
            <p>File: {this.state.file}</p>
            <button id='qs' onClick={this.queryServer}>Server</button>
        </div>);
  }
}

describe('Jest Create React Tests', function () {

    beforeEach(() => {
        global.fetch = jest.fn().mockImplementation(() => {
            const promise = new Promise((resolve, reject) => {
                resolve({
                    ok: true,
                    json: function () {
                        return {file: 'api.js'};
                    }
                });
            });
            return promise;
        });
    });

    it('renders test', () => {
        const wrapper = shallow(<App/>);
        const fileParagraph = <p>File: api.js</p>;
        wrapper.find('#qs').simulate('click');
        setImmediate(() => {
            wrapper.update();
            expect(wrapper.contains(fileParagraph)).toEqual(true);
        });
    });

});

try {
   expect(wrapper.contains(statusParagraph)).toBe(true);
} catch (e) {
   console.log(e);
}