Express-validator is a middleware for Express on Node.js that can help you validate user input. It’s a lovely library. Here’s a pattern for testing code that uses it.


To get express-validator in your project, install with npm:

npm install express-validator --save

Plug in the Middleware

To use the middleware in your code, crack open the part of your app that sets up Express middlewares, and add in a reference to this lil beaut:

expressValidator = require 'express-validator'

# ...

app.use express.json()
app.use expressValidator()

Note that you should insert the new express-validator middleware directly after the json middleware. Also note that the json middleware, used in conjunction with urlencoded now replace bodyParser to avoid deprecation warnings on startup.

Validate Something

Let’s say you’re writing a validator for new posts to a blog. That code might look like this.

module.exports = (req) ->

  req.checkBody('title', 'Title is required').notEmpty()
  req.checkBody('body', 'Body is required').notEmpty()

  !req.validationErrors() or req.validationErrors().length is 0

It checks to see if there is a title and a body given. If there is not, the validator will return false, and there will be a validation errors array on the req object. There are many other assertions (provided internally by validator.js) besides notEmpty that you can use.

Validating the Validator

First, setup a test helper that stubs the request, req, for validation:

expressValidator = require('express-validator')()

exports.stubForValidation = (done) ->
  req =
    query: {}
    body: {}
    params: {}
    param: (name) ->

  expressValidator req, {}, ->

There’s nothing too incredibly special here. It’s just abstracted out of your test into a reusable helper. The req object has empty objects to slap fixture data onto in your tests. It includes a stubbed param function that can return params by name. Finally, the express-validator middleware is called with the stubbed req object.

Now, in your test, you can simply:

  1. Stub the request before each test
  2. Setup your fixture data to make the test pass (or not)
  3. Assert validation errors’ existence and messages
stubReq = require('req').stubForValidation
validateNew = require 'blog-new-validator'

describe 'blog-new-validator', ->

  req = null

  beforeEach (done) ->
    stubReq (r) ->
      req = r

  it 'is invalid without title', ->
    req.validationErrors(true).title.msg.should.eql 'Title is required'

  it 'is invalid without body', ->
    req.validationErrors(true).body.msg.should.eql 'Body is required'

  it 'is valid with title and body', ->
    req.body.title = 'New Blog Title'
    req.body.body = 'The body of the blog.'

What do you think? Is there an easier way? A way to get better assertions?