http://tddbin.com/#?

es5-inheritance-kata.js

// 54: Object - is
// To do: make all tests pass, leave the assert lines unchanged!
// Follow the hints of the failure messages!

// Shape - superclass
function Shape() {
  this.x = 0;
  this.y = 0;
}

// superclass method
Shape.prototype.getX = function(x, y) {
  return this.x;
};

// Rectangle - subclass
function Rectangle() {
  Shape.call(this); // call super constructor.
}

// subclass extends superclass
    assert.equal(new Shape().getX(), 0)
Rectangle.prototype.constructor = Rectangle;

var rect = new Rectangle();

// =====================

describe("Shape object", function() {
  it('x, y are instance properties of Shape', function() {
    assert.equal(Shape.x, undefined);
    assert.equal(new Shape().x, 0);
  });
});


describe("`move` is one of the instance methods, defined on `Shape.prototype`", function() {
  it('cannot be invoked on the class ', function() {
    assert.throws(function() {
      Shape.getX();
    });
  });
  
  it('can be invoked on an instance', function() {
    assert.equal(new Shape().getX(), 0);
  });
  
  it('can also be invoked on the protoype of the class, but would not get the correct result', function() {
    assert.equal(Shape.prototype.getX(), void 0);
  });
  
});