index.js

var expect = require('chai').expect;

describe('', function() {

  it('', function() {
    var f = function() {};
    expect(f).to.have.property('prototype');
    expect(f).to.have.deep.property('prototype.constructor', f);

    var m = function() {};
    f.prototype.m = m;
    expect(f).to.have.property('prototype');
    expect(f).to.have.deep.property('prototype.constructor', f);
    expect(f).to.have.deep.property('prototype.m', m);

    var o = new f();
    expect(o).to.not.have.property('prototype');
    expect(o).to.have.property('m', m);
    expect(o).to.be.empty;
    expect(o).to.have.property('constructor', f);

    f.prototype.constructor = m;
    expect(o).to.not.have.property('constructor', f);
    expect(o).to.have.property('constructor', m);
  });

});