Test for using gulp.dest

This test highlight the issue with `gulp-tap` caching. If I remove caching or use [the argument caching scheme](https://github.com/dotnetCarpenter/gulp-tap/tree/memorize), the test pass.

Unfortunately, I can't get `npm test` to execute the coffee-script based test. But `nodeunit tests` works. I've [googled for an answer](https://www.google.com/webhp?q=npm+test+nodeunit+issue+coffeescript) and while others have had the same issue, it should be resolved. I'm clueless to why it doesn't work in this particular case.