Understanding Mocha Error Codes

In this tutorial we will be examining the error codes you can get while running a mocha test.

This feature is new in V6.0.0. when Mocha throws an error by itself, the associated Error has a code property. Where it is applicable, the consumers have to check the code property rather than string-matching against the message property. Below is a table that describes each of the erro codes.

'use strict';
/**
 * @module Errors
 */
/**
 * Factory functions that creates throwable error objects
 */

will create an error object to be thrown when no files to be tested could be found using specified pattern.

function createNoFilesMatchPatternError(message, pattern) {
  var err = new Error(message);
  err.code = 'ERR_MOCHA_NO_FILES_MATCH_PATTERN';
  err.pattern = pattern;
  return err;
}

will create an error object to be thrown when the reporter specified in the options was not found.

function createInvalidReporterError(message, reporter) {
  var err = new TypeError(message);
  err.code = 'ERR_MOCHA_INVALID_REPORTER';
  err.reporter = reporter;
  return err;
}

will create an error object to be thrown when the interface specified in the options was not found.

function createInvalidInterfaceError(message, ui) {
  var err = new Error(message);
  err.code = 'ERR_MOCHA_INVALID_INTERFACE';
  err.interface = ui;
  return err;
}

will create an error object to be thrown when a behavior, option, or parameter is unsupported.

function createUnsupportedError(message) {
  var err = new Error(message);
  err.code = 'ERR_MOCHA_UNSUPPORTED';
  return err;
}

will create an error object to be thrown when an argument is missing.

function createMissingArgumentError(message, argument, expected) {
  return createInvalidArgumentTypeError(message, argument, expected);
}

will create an error object to be thrown when an argument did not use the supported type

function createInvalidArgumentTypeError(message, argument, expected) {
  var err = new TypeError(message);
  err.code = 'ERR_MOCHA_INVALID_ARG_TYPE';
  err.argument = argument;
  err.expected = expected;
  err.actual = typeof argument;
  return err;
}

will create an error object to be thrown when an argument did not use the supported value

function createInvalidArgumentValueError(message, argument, value, reason) {
  var err = new TypeError(message);
  err.code = 'ERR_MOCHA_INVALID_ARG_VALUE';
  err.argument = argument;
  err.value = value;
  err.reason = typeof reason !== 'undefined' ? reason : 'is invalid';
  return err;
}

will create an error object to be thrown when an exception was caught, but the `Error` is falsy or undefined.

function createInvalidExceptionError(message, value) {
  var err = new Error(message);
  err.code = 'ERR_MOCHA_INVALID_EXCEPTION';
  err.valueType = typeof value;
  err.value = value;
  return err;
}
module.exports = {
  createInvalidArgumentTypeError: createInvalidArgumentTypeError,
  createInvalidArgumentValueError: createInvalidArgumentValueError,
  createInvalidExceptionError: createInvalidExceptionError,
  createInvalidInterfaceError: createInvalidInterfaceError,
  createInvalidReporterError: createInvalidReporterError,
  createMissingArgumentError: createMissingArgumentError,
  createNoFilesMatchPatternError: createNoFilesMatchPatternError,
  createUnsupportedError: createUnsupportedError
};