Function assertChanges

browser-version/test/chai.js:2393–2407

* ### .change(function) * * Asserts that a function changes an object property * * var obj = { val: 10 }; * var fn = function() { obj.val += 3 }; * var noChangeFn = function() { return 'foo' + 'bar'; } * expect(fn).to.change(obj, 'val'); * expect(noChangFn

(object, prop, msg)

   */

  function assertChanges (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(
      initial !== object[prop]
      , 'expected .' + prop + ' to change'
      , 'expected .' + prop + ' to not change'
    );
  }

  Assertion.addChainableMethod('change', assertChanges);
  Assertion.addChainableMethod('changes', assertChanges);