ES6 katas for Numbers - http://es6katas.org/

es6-numbers.js

// 55: Number - isInteger

describe('`Number.isInteger()` determines if a value is an integer', function(){

  const isTrue = (what) => assert.equal(what, true);
  const isFalse = (what) => assert.equal(what, false);

  it('`isInteger` is a static function on `Number`', function() {
    const whatType = 'function';
    assert.equal(typeof Number.isInteger, whatType);
  });

  describe('zero in different ways', function() {
    it('0 is an integer', function() {
      const zero = 0;
      isTrue(Number.isInteger(zero));
    });
    it('0.000', function() {
      isTrue(Number.isInteger(0.000));
    });
    it('the string "0" is NOT an integer', function() {
      const stringZero = '0';
      isFalse(Number.isInteger(stringZero));
    });
  });

  describe('one in different ways', function() {
    it('0.111 + 0.889', function() {
      const rest = 0.889;
      isTrue(Number.isInteger(0.111 + rest));
    });
    it('0.5 + 0.2 + 0.2 + 0.1 = 1 ... isn`t it?', function() {
      const oneOrNot = 0.5 + 0.2 + 0.2 + 0.1;
      isFalse(Number.isInteger(oneOrNot));
    });
    it('parseInt`ed "1" is an integer', function() {
      const convertedToInt = Number.parseInt('1.01');
      isTrue(Number.isInteger(convertedToInt));
    });
  });
  
  describe('what is not an integer', function() {
    it('`Number()` is an integer', function() {
      const numberOne = Number();
      isTrue(Number.isInteger(numberOne));
    });
    it('`{}` is NOT an integer', function() {
      const isit = Number.isInteger({});
      isFalse(isit);
    });
    it('`0.1` is not an integer', function() {
      const isit = Number.isInteger(0.1);
      isFalse(isit);
    });
    it('`Number.Infinity` is not an integer', function() {
      const isit = Number.isInteger(Number.Infinity);
      isFalse(isit);
    });
    it('`NaN` is not an integer', function() {
      const isit = Number.isInteger(NaN);
      isFalse(isit);
    });
  });

});