I am trying to ignore /tests/end-to-end and found this package but I'm having trouble getting it to work... What am I doing wrong?

This is my ember-cli-build.js

/*jshint node:true*/
/* global require, module */
var EmberApp = require('ember-cli/lib/broccoli/ember-app');
var unwatchedTree = require('broccoli-unwatched-tree');

module.exports = function(defaults) {
  var app = new EmberApp(defaults, {
    'ember-cli-bootstrap-sassy': {
      'quiet': true
    }
  });
  var casperTests = new unwatchedTree('tests/end-to-end');

  return app.toTree();
};

Please revert this deprecation and release as a patch. You can then add the deprecation and release on npm as a major release. This way the countless apps using this package do not break the next time they install, and the package still gets deprecated.

It broke because broccoli-source requires that you call new UnwatchedDir, whereas your package did not require this.