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

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.

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

Already answered but thought I would add that you can do this user winston.add()

var logger = new (winston.Logger)({
    transports: [
        new (winston.transports.File)({filename: 'node.log'})
    ]
});

if (process.env.NODE_ENV === 'test') {
    logger.add(winston.transports.Console, {prettyPrint: true});
}