Testing nodejs REST

Why testing?

• Does not prove the absence of bugs
• Can help identify existing bugs
• Can avoid introducing new bugs
• Repeated testing necessary in agile development
• Automated as far as possible
• It's in the assignment ...

Basic Approaches

• Using browser (manual)
• Using Postman (partly automatic)
• Using test scripts (automatic)

Browser-based testing

• GET is easy: just type in URL
• POST is slightly harder: build HTML form
• Other http methods more difficult

Postman

• Originally a chrome plugin
• Now a web/dekstop application
• Define a set of requests in a collection
• Choose GET or POST (or other)
• Include body parameters for POST
• Use raw/JSON for JSON
• Can specify expected responses

Test scripts

• There are very many JavaScript unit testing frameworks (mocha, jasmine, ava)
• I recommend using Jest
• Read a recent review
• Also see StateofJS
• npm install --save-dev jest
• Tests are js programs (as in jUnit)
• Put tests in test directory or name .test.js

Running tests

• Get it going first
• Use nodemon to auto-restart server
• Add test script to your package.json
• run test with npm test
• see some example tests for thing

Separate out app from server

So that running tests does not launch the server

e.g. app.js file

const express = require('express');
const app = express();
// ... add routes
module.exports = app;

e.g. server.js file

const app = require('./app');
app.listen(8090);

Test coverage

• In testing we try to improve quality
• Coverage measures how much functionality has been tested
• Could measure this in terms of
  • the space of possible inputs (black box)
  • the code that has been executed (white box)
• Unit testing combines the two
• Need to think about valid and invalid inputs

Mocking

• You want to avoid accessing live systems during tests
• Reading may be brittle
• Writing may be dangerous
• Real system may not be developed yet
• Replace access to live data using mocking
• There are specific jest functions for this
• If you intend to use a remote web service you should use mocking
• Same for a remote database (e.g. Firebase)