text: const expect = require('chai').expect;
  const linesCount = require('../src/tdd/async/files');
  
  describe('test server side callback', () => {
      it('should return correct lines count for a valid file', (done) => {
          const callback = (count) => {
              expect(count).to.be.eql(15);
              done();
          };
          
          linesCount('src/tdd/async/files.js', callback);
      });
  
      it('should report error for an invalid file name', (done) => {
          const onError = (error) => {
              expect(error).to.be.eql('unable to open file src/tdd/files.js');
              done();
          };
          linesCount('src/tdd/files.js', undefined, onError);
      });
  });