end = () => {
      if (!this.total && this._opts.failZero) this.failures = 1;

      debug('run(): root suite completed; emitting %s', constants$1.EVENT_RUN_END);
      this.emit(constants$1.EVENT_RUN_END);
    }
Run the root suite and invoke `fn(failures)`
on completion.

@public
@memberof Runner
@param {Function} fn - Callback when finished
@param {Object} [opts] - For subclasses
@param {string[]} opts.files - Files to run
@param {Options} opts.options - command-line options
@returns {Runner} Runner instance.