diff --git a/gulpfile.js b/gulpfile.js
index adad2ab8f9..0f310bf8ec 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -85,7 +85,8 @@ var angularBuilder = {
 var treatTestErrorsAsFatal = true;
 
 function runJasmineTests(globs, done) {
-  fork('./tools/traceur-jasmine', globs, {
+  var args = ['--'].concat(globs);
+  fork('./tools/traceur-jasmine', args, {
     stdio: 'inherit'
   }).on('close', function jasmineCloseHandler(exitCode) {
     if (exitCode && treatTestErrorsAsFatal) {
@@ -466,7 +467,7 @@ gulp.task('test.unit.cjs', ['build/clean.js', 'build.tools'], function (neverDon
 
 
 gulp.task('test.unit.tools/ci', function(done) {
-  runJasmineTests(['dist/tools/**/*.spec.js'], done);
+  runJasmineTests(['dist/tools/**/*.spec.js', 'tools/**/*.spec.js'], done);
 });
 
 
diff --git a/tools/build/watch.spec.js b/tools/build/watch.spec.js
new file mode 100644
index 0000000000..b1f06dce6b
--- /dev/null
+++ b/tools/build/watch.spec.js
@@ -0,0 +1,154 @@
+var rewire = require('rewire');
+
+describe('watch()', function() {
+  var timeout;
+  var watch;
+  var watcher;
+  var unmock;
+
+  beforeEach(function() {
+    timeout = mockTimeout();
+    var watchModule = rewire('./watch');
+    unmock = watchModule.__set__(timeout.mocks);
+    watch = watchModule.__get__('watch');
+  });
+
+  afterEach(function() {
+    // Shouldn't really be necessary, but...
+    if (watcher) {
+      watcher.close();
+      watcher = null;
+    }
+    unmock();
+    expect(timeout.pending).toBe(0);
+    timeout = null;
+  });
+
+
+  it('should fire callback once for events which occur within `delay` window', function() {
+    var cb = jasmine.createSpy('callback');
+    watcher = watch('./$$fake_path/**/*', { delay: 10 }, cb);
+
+    watcher._emit('add', './$$fake_path/test.txt');
+    timeout.flush(9);
+    expect(cb).not.toHaveBeenCalled();
+
+    watcher._emit('change', './$$fake_path/test.txt');
+    watcher._emit('add', './$$fake_path/test2.txt');
+    watcher._emit('change', './$$fake_path/test2.txt');
+    watcher._emit('add', './$$fake_path/test3.txt');
+    watcher._emit('change', './$$fake_path/test3.txt');
+    expect(cb).not.toHaveBeenCalled();
+
+    timeout.flush(1);
+    expect(cb.calls.count()).toBe(1);
+  });
+
+
+  it('should trigger callback if events are collected during task running', function() {
+    var calls = 0;
+    function cb(done) {
+      if (++calls !== 1) return done();
+
+      watcher._emit('change', './$$fake_path/test1.txt');
+      watcher._emit('change', './$$fake_path/test2.txt');
+
+      // Before the done callback, there are no pending timer events
+      expect(timeout.pending).toBe(0);
+      done();
+
+      // Afterwards, there is one
+      expect(timeout.pending).toBe(1);
+    }
+
+    var watcher = watch('./$$fake_path/**/*', { delay: 10 }, cb);
+
+    watcher._emit('change', './$$fake_path/test1.txt');
+    expect(timeout.pending).toBe(1);
+    expect(calls).toBe(0);
+
+    timeout.flush(10);
+    expect(calls).toBe(2);
+  });
+
+
+  it('should cancel pending callback if FSWatcher is closed', function() {
+    var cb = jasmine.createSpy('callback');
+    var watcher = watch('./$$fake_path/**/*', { delay: 10 }, cb);
+
+    watcher._emit('change', './$$fake_path/test1.txt');
+    expect(timeout.pending).toBe(1);
+    expect(cb).not.toHaveBeenCalled();
+
+    watcher.close();
+    expect(timeout.pending).toBe(0);
+  });
+
+
+  it('should cancel followup pending callback if FSWatcher is closed during task', function() {
+    var calls = 0;
+    function cb(done) {
+      if (++calls !== 1) return done();
+
+      watcher._emit('change', './$$fake_path/test2.txt');
+      done();
+      expect(timeout.pending).toBe(1);
+      watcher.close();
+      expect(timeout.pending).toBe(0);
+    }
+
+    var watcher = watch('./$$fake_path/**/*', { delay: 10 }, cb);
+    watcher._emit('change', './$$fake_path/test1.txt');
+
+    timeout.flush(10);
+
+    expect(calls).toBe(1);
+  });
+});
+
+
+// setTimeout/clearTimeout mocking, mostly stolen from angular-mocks.js
+function mockTimeout() {
+  var events = [];
+  var id = 0;
+  var now = 0;
+
+  return {
+    mocks: {
+      setTimeout: mockSetTimeout,
+      clearTimeout: mockClearTimeout
+    },
+    flush: flush,
+    get pending() { return events.length; }
+  };
+
+  function mockSetTimeout(fn, delay) {
+    delay = delay || 0;
+    events.push({
+      time: now + delay,
+      fn: fn,
+      id: id
+    });
+    events.sort(function(a, b) { return a.time - b.time; });
+    return id++;
+  }
+
+  function mockClearTimeout(id) {
+    for (var i = 0; i < events.length; ++i) {
+      if (events[i].id === id) {
+        events.splice(i, 1);
+        break;
+      }
+    }
+  }
+
+  function flush(delay) {
+    if (delay !== undefined) now += delay;
+    else if (events.length) now = events[events.length - 1].time;
+    else throw new Error('No timer events registered');
+
+    while (events.length && events[0].time <= now) {
+      events.shift().fn();
+    }
+  }
+}