mochajs/mocha · error · UnsupportedError

ERR_MOCHA_UNSUPPORTED

ERR_MOCHA_UNSUPPORTED

Error message

workerReporter() not supported in serial mode

What it means

Error "workerReporter() not supported in serial mode" thrown in mochajs/mocha.

Source

Thrown at lib/runner.cjs:1342

 * @public
 * @returns {false}
 */
Runner.prototype.isParallelMode = function isParallelMode() {
  return false;
};

/**
 * Configures an alternate reporter for worker processes to use. Subclasses
 * using worker processes should implement this.
 * @public
 * @param {string} path - Absolute path to alternate reporter for worker processes to use
 * @returns {Runner}
 * @throws When in serial mode
 * @chainable
 * @abstract
 */
Runner.prototype.workerReporter = function () {
  throw createUnsupportedError("workerReporter() not supported in serial mode");
};

/**
 * Filter leaks with the given globals flagged as `ok`.
 *
 * @private
 * @param {Array} ok
 * @param {Array} globals
 * @return {Array}
 */
function filterLeaks(ok, globals) {
  return globals.filter(function (key) {
    // Firefox and Chrome exposes iframes as index inside the window object
    if (/^\d+/.test(key)) {
      return false;
    }

    // in firefox

View on GitHub (pinned to 6bcbee4fd9)

When it happens

Trigger: Thrown at lib/runner.cjs:1342 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of mochajs/mocha@6bcbee4fd9 (2026-09-01). Data as JSON: /api/errors/86c97332a836c372. Report an issue: GitHub.