Proxable

Simple, unobtrosive function wrapper to allow for direct stubbing and spying. This is useful when writing tests for code that declares its dependencies using object destructuring or ESM import statements.

Returns the original function when NODE_ENV=production for zero overhead in production. This can be overruled by also setting PROXABLE=true.

Functions

createProxable(fn)

Takes a function fn to wrap (required).

Returns a wrapped function that proxies throught to fn by default.

Aliases: proxable(), create()

installStub(proxable, [stub])

Takes a wrapped proxable function (required) and a stub function or value.

• If stub is a function, it is installed as the proxable's' replacement function. function's original.
• If stub is any other value, a new function that returns the value stub is installed as the proxable's replacement.

Returns the replacement function.

Alias: stub()

installProxy(proxable, proxyMap)

Takes a wrapped proxable function (required) and a function that maps the original function to a replacement function (required).

Returns the replacement function.

Alias: proxy()

restoreOriginal(proxable)

Takes a wrapped proxable function (required) and restores its original behaviour.

Alias: restore()

Use case

What if you want to unit test the following code?

// users.js
 
const { find } = require('./database')
 
module.exports = {
  findUser (username) {
    return find('user', { name: username });
  }
}

You might want to stub out database.find using sinon (or similar). Normally you'd do something like this:

// users.test.js
 
const sinon = require('sinon')
const users = require('./users')
const database = require('./database')
 
sinon.stub(database, 'find')

But this won't work, since users.js has a direct reference to the orignal, unstubbed database.find:

const users.findUser('steve') 
assert.equal(database.find.callCount, 1) // !-> AssertionError [ERR_ASSERTION]: 0 == 1

That's where proxable comes in. By instrumenting database.find, you can stub or spy on it even for code that has a direct reference to it:

// database.js
 
const { createProxable } = require('proxable')
 
module.exports {
  find: createProxable(function find (table, params) {
    // [...]
  })
}

Which allows you to stub it in your test:

// users.test.js
 
const { installStub, restoreOriginal } = require('proxable')
const sinon = require('sinon')
const users = require('./users')
const database = require('./database')
 
installStub(database.find, sinon.stub())
 
const users.findUser('steve') 
assert.equal(database.find.callCount, 1) // -> OK
 
restoreOriginal(database.find)

License

Distributed under the ISC license (see LICENSE).