text: const createCalculator = require('./calculator').createCalculator;
  const expect = require('chai').expect;
  
  describe('calculator', () => {
      it ('should return value of the internal sum when get method is invoked', () => {
          const calculator = createCalculator();
          const expected = 0;
          const actual = calculator.get();
          expect(actual).to.be.eql(expected);
      });
  
      it ('should add number to current sum', () => {
          const calculator = createCalculator();
          calculator.add(2);
          const expected = 2;
          const actual = calculator.get();
          expect(actual).to.be.eql(expected);
      });
  
      it ('should parse and add number to current sum', () => {
          const calculator = createCalculator();
          calculator.add('2');
          const expected = 2;
          const actual = calculator.get();
          expect(actual).to.be.eql(expected);
      });
  
      it ('should subtract number to current sum', () => {
          const calculator = createCalculator();
          calculator.subtract(2);
          const expected = -2;
          const actual = calculator.get();
          expect(actual).to.be.eql(expected);
      });
  
      it ('should parse and subtract number to current sum', () => {
          const calculator = createCalculator();
          calculator.add('-2');
          const expected = -2;
          const actual = calculator.get();
          expect(actual).to.be.eql(expected);
      });
  
      it ('should return undefined when internal sum is modified', () => {
          const calculator = createCalculator();
          const actual = calculator.value;
          expect(actual).to.be.undefined;
      });
  });