function assertIncreases (object, prop, msg) {
    if (msg) flag(this, 'message', msg);
    var fn = flag(this, 'object');
    new Assertion(object, msg).to.have.property(prop);
    new Assertion(fn).is.a('function');

    var initial = object[prop];
    fn();

    this.assert(
      object[prop] - initial > 0
      , 'expected .' + prop + ' to increase'
      , 'expected .' + prop + ' to not increase'
    );
  }
### .increase(function)

Asserts that a function increases an object property

    var obj = { val: 10 };
    var fn = function() { obj.val = 15 };
    expect(fn).to.increase(obj, 'val');

@name increase
@alias increases
@alias Increase
@param {String} object
@param {String} property name
@param {String} message _optional_
@api public