When calling truffle test some_test.js, I would like to pass Mocha switches.

For example: truffle --no-colors test some_test.js works fine.

However: truffle --reporter json-streams test some_test.js doesn't.

To my understanding, it should get Mocha to generate all the output in JSON format.

Any ideas?

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I can do it by adding this to the Truffle configuration file (truffle.js or truffle-config.js):

mocha: {
    useColors: false,
    reporter: "json"

Available reporters are described here.

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  • But this is restricted to general configuration. What if a I want to use some mocha settings for my dev environment but others for CI? – jmendiola Aug 5 '19 at 17:22

Truffle uses Mocha programatically. So, the Mocha class constructor shows the full options. Truffle v5.1.9 seems to use Mocha v5.2.0 and the constructor code for this version can be found here.


Which shows

 * @class Mocha
 * @param {Object} options
function Mocha(options) {
  options = options || {};
  this.files = [];
  this.options = options;
  if (options.grep) {
    this.grep(new RegExp(options.grep));
  if (options.fgrep) {
  this.suite = new exports.Suite('', new exports.Context());
  this.reporter(options.reporter, options.reporterOptions);
  if (typeof options.timeout !== 'undefined' && options.timeout !== null) {
  if (typeof options.retries !== 'undefined' && options.retries !== null) {
  if (options.enableTimeouts !== null) {
  if (options.slow) {

You can find options like ui, bail, reporter, reporterOptions, timeout, retries, useColors, enableTimeouts and so on.

More detailed meaning of these options can be inferred from the API documentation of Mocha class located at https://mochajs.org/api/mocha.

For example, API documentations for methods such as bail(), retries(), enableTimeouts(), or timeout() show more details on corresponding options.

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