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.go

@@ -0,0 +1,94 @@
+package gocui
+
+// A task represents the fact that the program is busy doing something, which
+// is useful for integration tests which only want to proceed when the program
+// is idle.
+
+type Task interface {
+	Done()
+	Pause()
+	Continue()
+	// not exporting because we don't need to
+	isBusy() bool
+}
+
+type TaskImpl struct {
+	id        int
+	busy      bool
+	onDone    func()
+	withMutex func(func())
+}
+
+func (self *TaskImpl) Done() {
+	self.onDone()
+}
+
+func (self *TaskImpl) Pause() {
+	self.withMutex(func() {
+		self.busy = false
+	})
+}
+
+func (self *TaskImpl) Continue() {
+	self.withMutex(func() {
+		self.busy = true
+	})
+}
+
+func (self *TaskImpl) isBusy() bool {
+	return self.busy
+}
+
+type TaskStatus int
+
+const (
+	TaskStatusBusy TaskStatus = iota
+	TaskStatusPaused
+	TaskStatusDone
+)
+
+type FakeTask struct {
+	status TaskStatus
+}
+
+func NewFakeTask() *FakeTask {
+	return &FakeTask{
+		status: TaskStatusBusy,
+	}
+}
+
+func (self *FakeTask) Done() {
+	self.status = TaskStatusDone
+}
+
+func (self *FakeTask) Pause() {
+	self.status = TaskStatusPaused
+}
+
+func (self *FakeTask) Continue() {
+	self.status = TaskStatusBusy
+}
+
+func (self *FakeTask) isBusy() bool {
+	return self.status == TaskStatusBusy
+}
+
+func (self *FakeTask) Status() TaskStatus {
+	return self.status
+}
+
+func (self *FakeTask) FormatStatus() string {
+	return formatTaskStatus(self.status)
+}
+
+func formatTaskStatus(status TaskStatus) string {
+	switch status {
+	case TaskStatusBusy:
+		return "busy"
+	case TaskStatusPaused:
+		return "paused"
+	case TaskStatusDone:
+		return "done"
+	}
+	return "unknown"
+}