function assertLength (n, msg) {
    if (msg) flag(this, 'message', msg);
    var obj = flag(this, 'object');
    new Assertion(obj, msg).to.have.property('length');
    var len = obj.length;

    this.assert(
        len == n
      , 'expected #{this} to have a length of #{exp} but got #{act}'
      , 'expected #{this} to not have a length of #{act}'
      , n
      , len
    );
  }
### .lengthOf(value[, message])

Asserts that the target's `length` property has
the expected value.

    expect([ 1, 2, 3]).to.have.lengthOf(3);
    expect('foobar').to.have.lengthOf(6);

@name lengthOf
@param {Number} length
@param {String} message _optional_
@namespace BDD
@api public