Refactor our test after import the exercise builder

ExerciseDetail.spec.tsx

import { shallow } from 'enzyme';
import * as React from 'react';
import { ExerciseDetail } from './';
import { createAnExercise } from './ExerciseMockBuilder'

describe('ExerciseDetail', () => {
  it('should display the warning when it\'s present in the exercise', () => {
    const anExercise: Exercise = createAnExercise({warning: 'a warning message'})
    const wrapper = shallow(<ExerciseDetail exercise={anExercise}/>);
    const message = wrapper.find('Message');

    expect(message.exists()).toBeTruthy();
  });
  
  it('should not display the warning when it\'s not set in the exercise', () => {
    const anExercise: Exercise = createAnExercise({warning: null})
    const wrapper = shallow(<ExerciseDetail exercise={anExercise}/>);
    const message = wrapper.find('Message');

    expect(message.exists()).toBeFalsy();
  });

  it('should render a list multiple tags', () => {
    const someTags = ['irrelevant tag 1', 'irrelevant tag 2']
    const anExercise: Exercise = createAnExercise({tags: someTags})
    const wrapper = shallow(<ExerciseDetail exercise={anExercise}/>);
    const chips = wrapper.find('Chip');

    expect(chips.length).toBe(someTags.length);
  });

});