TDD MOOC: Untestable Code

This is an exercise for learning about unit testing and writing testable code.

You have been given four examples of untestable or at least hard-to-test code. See the src and test directories. The examples are numbered 1 to 4, in order of difficulty.

First determine that what things make the code examples hard to test. (See Chapter 3 of the course material.) Write your learnings as comments in the untestable code.

Then create a copy of the untestable code, refactor it to be easily testable, and write tests for it.

P.S. If you want an extra challenge, also write tests for the original untestable code. Then compare the tests you wrote for the refactored code and the original code, and see how much more complicated they are.

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This exercise is part of the TDD MOOC at the University of Helsinki, brought to you by Esko Luontola and Nitor.

Prerequisites

You'll need a recent Node.js version. Then download this project's dependencies with:

npm install

Part 4 of this exercise provides Docker configuration for starting the database, but you may also run PostgreSQL without containers.

Developing

Start the database (used by untestable4)

docker compose up -d

This will start a PostgreSQL 13 database to which you can connect using the following settings:

• Host: localhost
• Port: 5432
• User: untestable
• Password: secret
• Database: untestable
• It will also create a users table in the public schema based on src/create-tables.sql

Stop and destroy the database

docker compose down

Run tests once

npm run test

Run tests continuously

npm run autotest

Code reformat

npm run format