Use an interface for tasks instead of a concrete struct

By using an interface for tasks we can use a fake implementation in tests with extra methods

vendor/github.com/jesseduffield/gocui/task_manager.go

@@ -0,0 +1,67 @@
+package gocui
+
+import "sync"
+
+// Tracks whether the program is busy (i.e. either something is happening on
+// the main goroutine or a worker goroutine). Used by integration tests
+// to wait until the program is idle before progressing.
+type TaskManager struct {
+	// each of these listeners will be notified when the program goes from busy to idle
+	idleListeners []chan struct{}
+	tasks         map[int]Task
+	// auto-incrementing id for new tasks
+	nextId int
+
+	mutex sync.Mutex
+}
+
+func newTaskManager() *TaskManager {
+	return &TaskManager{
+		tasks:         make(map[int]Task),
+		idleListeners: []chan struct{}{},
+	}
+}
+
+func (self *TaskManager) NewTask() *TaskImpl {
+	self.mutex.Lock()
+	defer self.mutex.Unlock()
+
+	self.nextId++
+	taskId := self.nextId
+
+	onDone := func() { self.delete(taskId) }
+	task := &TaskImpl{id: taskId, busy: true, onDone: onDone, withMutex: self.withMutex}
+	self.tasks[taskId] = task
+
+	return task
+}
+
+func (self *TaskManager) addIdleListener(c chan struct{}) {
+	self.idleListeners = append(self.idleListeners, c)
+}
+
+func (self *TaskManager) withMutex(f func()) {
+	self.mutex.Lock()
+	defer self.mutex.Unlock()
+
+	f()
+
+	// Check if all tasks are done
+	for _, task := range self.tasks {
+		if task.isBusy() {
+			return
+		}
+	}
+
+	// If we get here, all tasks are done, so
+	// notify listeners that the program is idle
+	for _, listener := range self.idleListeners {
+		listener <- struct{}{}
+	}
+}
+
+func (self *TaskManager) delete(taskId int) {
+	self.withMutex(func() {
+		delete(self.tasks, taskId)
+	})
+}