Set up your project

0. Clone this git repository

   • In your profile > settings > SSH Keys confirm you have set up an SSH Key for Github. If not, then set up SSH access to github. Connecting to GitHub with SSH

1. Install Node.js (v8.1.4 or above)

   • Mac/Linux: Install nvm from https://github.com/creationix/nvm, then run nvm use from your terminal
   • Windows: Download and install Node.js from https://nodejs.org/en/download/

2. From your terminal, run npm init -y

Install Jest

Jest is a JavaScript test framework that we can use for testing both front-end and back-end code.

One of Jest's philosophies is to provide an integrated "zero-configuration" experience for writing tests. Conveniently, this means that it includes everything you need for TDD in a single package (test runner, assertions, matchers, spies, stubs and mocks)

The jest documentation can be found here: https://jestjs.io/docs/en/getting-started

1. Install jest with npm install --save-dev jest

2. Modify your package.json file, replacing:

   "scripts": {
       "test": "echo \"Error: no test specified\" && exit 1"
   },
   

   with

   "scripts": {
       "test": "jest --verbose",
       "tdd": "jest --verbose --watch --onlyChanged"
   },
   

3. Run npm test

   This command runs all tests and exits. Typically, we will call this from within the build pipeline.

4. Run npm run tdd

   This command continuously watches files for changes and rerun tests related to changed files. This is the command we will be using most often during TDD.

Configure pre-commit hooks [Optional]

To prevent bad commits, we can configure pre-commit hooks to ensure that unit tests are run before every commit.

1. Install husky with npm install --save-dev husky

2. Modify your package.json file, replacing:

   "scripts": {
       "test": "jest --verbose",
       "tdd": "jest --verbose --watch --onlyChanged"
   },
   
   

   with

   "scripts": {
       "test": "jest --verbose",
       "tdd": "jest --verbose --watch --onlyChanged",
       "precommit": "npm test"
   },
   
   

Configure your IDE [Optional]

IntelliJ

In Preferences:

1. Under Language & Frameworks > JavaScript, set your JavaScript language version to "ECMAScript 6".

2. Under Language & Frameworks > JavaScript > Libraries, download and enable both jest and node.

Explore the canary test

Open up server/00-canary/canary.spec.js, and note that:

1. For jest to find your tests, you need to place your tests in a __tests__ folder, or name your test files with a .spec.js or .test.js extension.

2. describe creates a block that groups together several related tests in one "test suite".

   You can also nest describe blocks if you have a hierarchy of tests.

3. it takes two arguments. The first argument describes the test; the second argument is a function that contains the expectations to test.

4. When you're writing tests, you often need to check that values meet certain conditions. expect gives you access to a number of "matchers" that let you validate different things.

   A good introduction to the available matchers can be found here: https://facebook.github.io/jest/docs/en/using-matchers.html

5. Together, the descriptions that we use in the describe and it blocks are shown in the test output. The aim is to structure and name our tests in such a way that the test output reads like a "requirements spec".

Let's get started!

Now that you're all set, let's get started with the TDD exercises.

As you go through the TDD exercises, keep in mind the Four Rules of Simple Design, and the Transformation Priority Premise.

The Four Rules of Simple Design:

• Passes the tests
• Reveals intention
• No duplication
• Fewest elements

The Transformation Priority Premise:

(01) [{} –> nil] no code => return nil

(02) [nil->constant] nil => simple constant

(03) [constant->constant+] simple constant => complex constant

(04) [constant->scalar] complex constant => variable or an argument

(05) [statement->statements] adding more unconditional statements.

(06) [unconditional->if] splitting the execution path

(07) [scalar->array]

(08) [array->container]

(09) [statement->recursion]

(10) [if->while]

(11) [expression->function] replacing an expression with a function or algorithm

(12) [variable->assignment] replacing the value of a variable.

Simplified Transformation Priority Premise:

(01) constant => a value

(02) scalar => a local binding, or variable

(03) invocation => calling a function/method

(04) conditional => if/switch/case/cond

(05) while loop => applies to for loops as well

(06) assignment => replacing the value of a variable