chai expect error code example

Example 1: mocha should throw error

describe('createMap', () => {
    it('should throw an error if no contents were sent as argument', () => {
      expect(() => createMap()).to.throw('You have to send a list of things to map.');
    });
  });

Example 2: what does chai expect return

Object.prototype.b = 2;

expect({a: 1}).to.have.own.property('a');
expect({a: 1}).to.have.property('b');
expect({a: 1}).to.not.have.own.property('b');

expect({a: 1}).to.own.include({a: 1});
expect({a: 1}).to.include({b: 2}).but.not.own.include({b: 2});

Example 3: chai expect to be type array

expect([1, 2]).to.be.an('array');