function assertInstanceOf (constructor, msg) {
        if (msg) flag(this, 'message', msg);
        var name = _.getName(constructor);
        this.assert(
            flag(this, 'object') instanceof constructor
          , 'expected #{this} to be an instance of ' + name
          , 'expected #{this} to not be an instance of ' + name
        );
      }
### .instanceof(constructor)

Asserts that the target is an instance of `constructor`.

    var Tea = function (name) { this.name = name; }
      , Chai = new Tea('chai');

    expect(Chai).to.be.an.instanceof(Tea);
    expect([ 1, 2, 3 ]).to.be.instanceof(Array);

@name instanceof
@param {Constructor} constructor
@param {String} message _optional_
@alias instanceOf
@api public