Add specs for Task events

Signed-off-by: Nathan Sobo <nathan@github.com>

spec/fixtures/task-spec-handler.coffee

@@ -1,2 +1,3 @@
 module.exports = ->
+  emit("some-event", 1, 2, 3)
   'hello'

spec/task-spec.coffee

@@ -20,3 +20,26 @@ describe "Task", ->
         expect(handlerResult).toBe 'hello'
         expect(childProcess.kill).toHaveBeenCalled()
         expect(processErrored).toBe false
+
+  it "calls listeners registered with ::on when events are emitted in the task", ->
+    task = new Task(require.resolve('./fixtures/task-spec-handler'))
+
+    eventSpy = jasmine.createSpy('eventSpy')
+    task.on("some-event", eventSpy)
+
+    waitsFor (done) -> task.start(done)
+
+    runs ->
+      expect(eventSpy).toHaveBeenCalledWith(1, 2, 3)
+
+  it "unregisters listeners when the Disposable returned by ::on is disposed", ->
+    task = new Task(require.resolve('./fixtures/task-spec-handler'))
+
+    eventSpy = jasmine.createSpy('eventSpy')
+    disposable = task.on("some-event", eventSpy)
+    disposable.dispose()
+
+    waitsFor (done) -> task.start(done)
+
+    runs ->
+      expect(eventSpy).not.toHaveBeenCalled()