Test cases getting failed when trying to do with mocha and chai

I am trying simple test cases using mocha framework

I have written simple typescript

    class Rectangle {

  constructor(width, height) {
    this.width = width;
    this.height = height;
  }

  get height() {
    return this.height;
  }

  set height(value) {
    if (typeof value !== 'number') {
      throw new Error('"height" must be a number.');
    }

    this.height = value;
  }

  get width() {
    return this.width;
  }

  set width(value) {
    if (typeof value !== 'number') {
      throw new Error('"width" must be a number.');
    }

    this.width = value;
  }


  get area() {
    return this.width * this.height;
  }


  get circumference() {
    return 2 * this.width + 2 * this.height;
  }
}
var rectangle= new Rectangle(10,20);
module.exports = Rectangle;

but when trying to write test case as below:

 "use strict"
    require('babel-register')({
        presets: ['es2015']
    });
    // Import chai.
    import * as chai from 'chai';
    var path = require('path');

    // Import the Rectangle class.
    let Rectangle = require(path.join(__dirname, '..', 'rectangle.js'));
    const should = chai.should;
    var expect = require('chai').expect;
    describe('Rectangle', () => {
        describe('#width', () => {
            let rectangle;

            beforeEach(() => {
                // Create a new Rectangle object before every test.
                rectangle = new Rectangle(10, 20);
            });

            it('returns the width', () => {
                // This will fail if "rectangle.width" does
                // not equal 10.
                rectangle.width.should.equal(10);
            });

        });
    });

but the test case is failing

I dont understand the error here

Any help would be appreciated