docs: function Runnable(title, fn) {
    this.title = title;
    this.fn = fn;
    this.body = (fn || '').toString();
    this.async = fn && fn.length;
    this.sync = !this.async;
    this._timeout = 2000;
    this._slow = 75;
    this._enableTimeouts = true;
    this.timedOut = false;
    this._retries = -1;
    this._currentRetry = 0;
    this.pending = false;
  }