How to suppress application logging messages from a node.js application when running unit tests?

Question

While unit-testing my node.js application (which is basically a REST backend) using mocha and supertest, I need only the test-specific message on the screen, but the stdout is also cluttered with application log messages.

I start the unit test with:

mocha -R spec . 

... and get this output (this is what it should not be):

[App] Listening on port 3000 ... [App] Starting app, hooray!    Project API     GET /projects [App] entering "projects" module ...       √ should return an array of projects (317ms) 

I marked the application log message with [App]. What I really want would be this output from the unit test:

  Project API     GET /projects       √ should return an array of projects (317ms) 

How can I suppress console.log/warn/error output by the application interspersed with Mocha's reporter output?

SOLUTION:

Following dankohn's approach, I ended up like this, which solves my issue (using winston for logging):

(in node's "main" server file, server.js:)

if (process.env.NODE_ENV !== 'test') {     logger = new (winston.Logger)({         transports: [             new (winston.transports.Console)(),             new (winston.transports.File)({ filename: 'foo.log' })         ]     }); } else {     // while testing, log only to file, leaving stdout free for unit test status messages     logger = new (winston.Logger)({         transports: [             new (winston.transports.File)({ filename: 'foo.log' })         ]     }); } 

... and to set the env variable, each unit test file starts with:

process.env.NODE_ENV = 'test'; 

Answer 1

In your app.js:

if (process.env.NODE_ENV !== 'test') {   app.use(express.logger()); } 

At the top of each of your mocha files:

process.env.NODE_ENV = 'test'; 

Update:

We use this function in our import code:

function logExceptOnTest(string) {   if (process.env.NODE_ENV !== 'test') {     console.log(string);   } } 

Then, replace all your console.log('it worked') with logExceptOnTest('it worked'). The basic trick is to use environment variables as a global flag as to the level of logging you want.

Answer 2

Here's a pretty simple solution that uses SinonJS's test stubs to suppress all console.log/info/warn/error statements before running your tests.

// my-method.js  export function myMethod() {     console.log(`I'm about to return true`)     return true } 

---

// my-method.test.js  import {describe, it, before} from 'mocha' import chai from 'chai' import sinon from 'sinon' import chalk from 'chalk' import {myMethod} from './my-method.js'  const expect = chai.expect  describe(chalk.underline('My Test Group'), () => {      before(() => {         sinon.stub(console, 'log')  // disable console.log         sinon.stub(console, 'info')  // disable console.info         sinon.stub(console, 'warn')  // disable console.warn         sinon.stub(console, 'error')  // disable console.error     })      describe('myMethod', () => {         it('should return true', () => {             expect(myMethod()).to.be.true  // without printing to the console         })     }) }) 

---

// output  My Test Group   myMethod     ✓ should return true