cancel () {
    this.cancelled = true
    if (this.runningCommand && typeof this.runningCommand[cancel] === 'function') {
      // We expect that cancelling this command will resolve the `run` promise.
      this.runningCommand[cancel]()
      if (typeof this.cancelSignal === 'function') {
        this.cancelSignal()
        this.cancelSignal = null
      }
      this.runningCommand = null
    }
  }
Cancels all commands in the commandRunner.