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farso is an HTTP mocking library for nodeJS.

farso is mainly used to craft e2e/human tests of HTTP services.

How does it work?

farso is made for developers and avoid the use of tons of json files to setup mocks, it offers a comprehensive DSL and a low level api based on expressjs so developers can precisely tweak their mock services to their needs where DSL do not cover use cases.

Mocking with farso invite you to travel in different vibes!

First of all, you have to define endpoints (destinations) you want to mock.

Then define all the vibes (scenarios) of your farso.

A vibe is made of mocks (mocked endpoints). Definition of mocks are inspired by nock

farso library is bundled with an http server api (also bin script) to run your vibes.

Then manually or from your testing framework you can select the desired vibe and request endpoints, farso will try to select an eligible mock and execute it. Because many mocks can be associated to an endpoint, farso will in the order of definition run the first that matches (see check methods below). If no eligible mock matches in current vibe farso will search in the default vibe to look for one.

Run tests on it, change the vibe and ...


$ npm install farso

farso at first glance

Let's say your system is using a CRM backoffice with an HTTP API offering an endpoint GET /public/v0/people.

You have to mock this endpoint.

First install farso, then add config files below:

// ./endpoints.js

const { endpoint } = require('farso');
endpoint('people', { uri: '/public/v0/people', method: 'get' });

// vibes.js
const { vibe } = require('farso');
const faker = require('faker');
const people = [
  {id: 1, name: faker.name.lastName()},
  {id: 2, name: faker.name.lastName()},

vibe.default('Main', mock => {
    .checkHeader({ 'x-corporis': /^\d+-\w+$/ })
    .reply([200, people]);

// farso.config.js
module.exports = {
  host: 'localhost',
  // port: 8181,
  vibes: path.join(__dirname, './vibes.js'),
  endpoints: path.join(__dirname, './endpoints.js'),

Then run:

$ DEBUG=farso* npx farso-server --config ./farso.config.js 
  farso Creating Vibe 'Main'
  farso Endpoint 'people:/public/v0/people' created
  farso Vibe 'Main' is now active
  farso server started on 'http://localhost:33811'

And now:

$ curl http://localhost:33811/public/v0/people

Here it is, you made your first farso mock.



With DSL api we will use the embendded server and will setup farso library with setup files like above sample.

config file must export and object with those properties:

  • host: default to localhost
  • port: optional, server's binding port, when no set server will bind dynamically to an available port
  • bodySizeLimit: see limit property
  • errorCode: optional, http status code to return when an endpoint matches without a mock.
  • vibes: glob partern to select vibe's files to load (see below) ex : path.join(__dirname, './data/**/*.vibes.js') or just path.join(__dirname, './vibes.js')
  • endpoint: glob partern to select endpoint's files to load (see below)
  • globals: optional, data injected to vibes (see below) to share states between http calls and vibes.
const path = require('path');
const faker = require('faker');

module.exports = {
  host: 'localhost',
  port: 8181,
  vibes: path.join(__dirname, './mock/**/*.vibe.js'),
  endpoints: path.join(__dirname, './mock/endpoints.js'),
  globals: {
    api: {
      clientId: faker.random.uuid(),
      clientSecret: faker.random.uuid(),

farso's server must be launched with: $ DEBUG=farso* npx farso-server --config ./farso.config.js

Server can be also setup and launched thanks { initTrip, initServer, runServer } functions exported from 'farso-mock/server' (see Low Level API section below)


endpoint files are used to define ..., endpoints, aka expressjs routes.

    const { endpoint } = require('farso-mock');
    endpoint('people:list', { uri: '/public/v0/people', method: 'get' });
    endpoint('people:get', { uri: '/public/v0/people/:id', method: 'get' });
    endpoint('people:create', { uri: '/public/v0/people', method: 'post' });
    endpoint('people:update', { uri: '/public/v0/people/:id', method: 'patch' });

ex: First call to endpoint will register an expressjs route on GET '/public/v0/people'

function endpoint(name, params)

  • name: String to identify an endpoint
  • params:
    • uri: endpoint's path
    • method: optional, endpoint's http method name
    • use: optional, expressjs middleware(s) associated with endpoint, could be useful to serve static files or code specific behaviour like endpoint('configs', { uri: '/configs', use: express.static(path.join(__dirname, './')) });


endpoints are useless without vibe, an endpoint will be associated with many vibes made of mocks:

const personSchema = { 
    firstname: /\w+/,
    lastname: /\w+/
vibe('Main', (mock, {globals: { api: { clientId, clientSecret } } }) => { 
    mock('people:list').reply([200, people]);
    mock('people:get').checkParams({ id: /\d+/ }).reply([200, person]);
    mock('people:create').checkBoby(personSchema).reply([200, person]);
    mock('people:update').checkParams({ id: /\d+/ }).checkBoby(personSchema).reply([200, person]);

function vibe(name, fn, options) or vibe.default(name, fn)

  • name: String must match an existing endpoint
  • options: { isDefault }, set vibe as default
  • fn: function(mock, { globals, lget, lvalue })
    • mock: function to define new mocks (see below)
    • globals: config's globals property
    • lget: function(String|Array): Object (see below)
    • lvalue: function(String|Array): Object (see below)

returns the current farso.

A default vibe will become the current one to search mocks, to switch to another one use farso#select(name) or HTTP API.

When a non default vibe is selected, eligible mocks are first searched in former vibe then in the default one.

farso's server offers a minimalist http api to list existing vibes:

$ curl http://[host:port]/_vibes_
    currentVibe: "Main",
    vibes: [
        "Main", "Wrong_auth"

and select one:

$ curl http://[host:port]/_vibes_/Wrong_auth
    currentVibe: "Wrong_auth"


A mock defines the behaviour of an endpoint:

vibe('V1', mock => mock('people:list').reply(200));

Requesting endpoint 'people:list' will return HTTP status code 200.

We can define many mocks per endpoint:

vibe('V1', mock => {
    mock('people:get').reply([200, person]);

or like this:

vibe('V1', mock => mock('people:list').reply(200));
vibe('V1', mock => 	mock('people:get').reply([200, person]));

We can define many mocks for the same endpoint:

vibe('V1', mock => mock('people:get').checkParams({ id: '12'}).reply([200, person]));
vibe('V1', mock => 	mock('people:get').checkParams({ id: '13'}).reply(404));

Order of definition matters.

We can define many mocks for the same endpoint in many vibes, in case you overwrite a mock already defined in the default endpoint, former wil be used. With a default vibe, an eligible mock is first look into current vibe, then if not found, in the default one.


Check url params

Ex: param id

endpoint('people:get', { uri: '/public/v0/people/:a/:b', method: 'get' });
vibe('V1', mock =>  {
        .checkParams({ a: '12', b: '13'})
        .checkParams({ a: /\d+/ b: :\w+X$/})
        .checkParams(({ a }) => Number(a) < 5)

endpoint's uri property use expressjs route's syntax definition.

function checkParams(options)

  • options: Object | Function
    • Object: if key/value do not match req.params mock will not be eligible, values can be a String or a RegExp
    • Function: function(params): Boolean, if returns false mock will not be eligible.

returns the current mock.


Check that requested headers match request.

function checkHeaders(options)

  • options: Object | Function
    • Object: if key/value do not match sent headers mock will not be eligible, values can be a String or a RegExp, keys are converted to lower case.
    • Function: function(headers): Boolean, if it returns false mock will not be eligible.


Check that requested query match request.

function checkQuery(options)

  • options: Object | Function
    • Object: if key/value do not match req.body mock will not be eligible, values can be a String or a RegExp.
    • Function: function(query): Boolean, if it returns false mock will not be eligible.


Check that requested body match request.

function checkBody(options)

  • options: Object | Function
    • Object: if key/value do not deeply match req.query mock will not be eligible, values can be a String or a RegExp. Object can be a nested object, is this case comparaison will be made using farso.deepMatch.
    • Function: function(body): Boolean, if it returns false mock will not be eligible.


Function executed when a mock is eligible.

function reply(options)

  • options: Number | Function | Array
    • Number: status code to return: res.sendStatus(options)
    • Array: [status, data]: res.status(options[0]).send(options[1])
    • Function: function(req, res)

returns current mock


lset/lget/lvalue allow to manage a local context between requests for the current vibe.

We can share global data thanks to globals prop in config and use it in vibes definition:

// farso.config.js
const path = require('path');
const faker = require('faker');

module.exports = {
  host: 'localhost',
  port: 8181,
  vibes: path.join(__dirname, './examples/**/*.vibe.js'),
  endpoints: path.join(__dirname, './examples/endpoints.js'),
  globals: {
    api: {
      clientId: faker.random.uuid(),
      clientSecret: faker.random.uuid(),

// main.vibe.js

vibe('Main', (mock, globals)  => { 
    mock('people:list').reply((req, res) => {
        globals.propA = valueA;

But to avoid dirty side effect here comes lset/lget/lvalue:

vibe.default('Main', (mock, { lget, globals: { token }}) => {

    .lset(({ body }) => [['data', 'firstname'], body.firstname])
    .lset(({ body }) => [['data', 'lastname'], body.lastname])
    .reply([201, token]);

  const req_create_claim = {
    firstname: lget['data', 'firstname']),
   	lastname: lget(['data', 'lastname']),

    .lset(({ body }) => [['data', 'claim'], body])

function lget(fn)

  • fn: function(Object): Object, returns a getter on current vibe's locals use case: lget(['data', 'lastname')) returns a getter on farso.currentVibe.locals.data.lastname getter will be evaluated by checker (check* methods)

function lset(fn)

  • fn: function(req): returns [path, value] Use case : mock('token').lset(({ body }) => [['data', 'firstname'], body.firstname]) will exec farso.currentVibe.locals.data.firstname = body.firstname

function lvalue(fn)

  • fn: function(Object): Object, returns value from current vibe's locals use case: lvalue(['data', 'lastname')) returns lget(['data', 'lastname')).value


Since version 1.2.0 farso allow to mock GraphQL queries/mutations

First define an endpoint:

// cat ./schema.graphql
type Query {
  echo(message: String): String
import { GraphQL } rom 'farso/graphql');
const schema = join(__dirname, './schema.graphql');
endpoint('graphql', { uri: '/graphql', use: GraphQL({ schemaPath: schema }) });                                

GraphQL endpoints use a special middleware GraphQL, with the path of our graphql's schema.

Then mock in vibes:

vibe.default('main', mock => {
  const mocks = {
    Query: () => ({
      echo: (_, { message }) => message,

Mocking is made at resolver level and use addMocksToSchema

Unlike HTTP mocks, we cannot define many mocks for a single endpoint in one vibe, onlu first call of resolve will be used.

You can get a full example in __tests__/graphql.test.js

Low level API


farso server can be launched thanks to farso-server script, like:

$ DEBUG=farso* npx farso-server --config ./farso.config.js

But also with API entries, it could be useful if we want to start a mock server within test and not before:

const { runServer } = require('farso/server');

let farsoServer;

const config = {
  vibes: path.join(__dirname, '../../examples/api.vibe.js'),
  endpoints: path.join(__dirname, '../../examples/endpoints.js'),

beforeAll(() => runServer(config).then(({ server }) => (farsoServer = server)));
afterAll(() => farsoServer.close());


We can dynamically register endpoints and create vibes, see unit tests for different samples.

const { initServer } = require('farso/server');
const Farso = require('farso');

let ctx;
let farso;
const initFarso = () => {
  farso = Farso({ errorCode });
  farso.createEndpoint('test', { uri: '/test', method: 'post' });
  return Promise.resolve({ farso });

beforeAll(() =>
    .then(c => (ctx = c)));
afterAll(() => ctx.server.close());

describe('...', () => {
  it('should ...', () => {
      .createVibe('v1', mock => mock('test').reply(200))
    return axios({ method: 'post', url: `${ctx.server.url}/test` });

That's all folks...

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