NI Dev Conference
Code and Slides for inaugural Northern Ireland Developer Conference talk https://www.nidevconf.com/
Slides from talk as Open Document Presentation file and PDF
Step by step instructions to recreate kata.
Create new directory
mkdir ni_dev_conf
Change into the new directory
cd ni_dev_conf
Initialize
npm init
Example:
This utility will walk you through creating a package.json file.
It only covers the most common items, and tries to guess sensible defaults.
See `npm help json` for definitive documentation on these fields
and exactly what they do.
Use `npm install <pkg> --save` afterwards to install a package and
save it as a dependency in the package.json file.
Press ^C at any time to quit.
name: (ni_dev_conf)
version: (1.0.0)
description: node version of prime factors kata done by uncle bob at ndc 2014
entry point: (index.js) factorsOf.js
test command: node node_modules/.bin/mocha
git repository:
keywords: prime factors kata uncle bob nidevconf nidevconf17
author: Diarmaid McGowan
license: (ISC)
About to write to /home/diarmaid/ni_dev_conf/package.json:
{
"name": "ni_dev_conf",
"version": "1.0.0",
"description": "node version of prime factors kata done by uncle bob at ndc 2014",
"main": "factorsOf.js",
"scripts": {
"test": "node node_modules/.bin/mocha"
},
"keywords": [
"prime",
"factors",
"kata",
"uncle",
"bob",
"nidevconf",
"nidevconf17"
],
"author": "Diarmaid McGowan",
"license": "ISC"
}
Is this ok? (yes)
Install mocha and chai as devDependencies
npm install --save-dev mocha chai or shorthand npm i -D mocha chai
Create test directory
mkdir test
Create empty test file
touch test/factorsOf_test.js
Open the folder in Visual Studio Code
You can download and install from https://code.visualstudio.com/
Start writing our first test
I am using chai for the BDD style http://chaijs.com/guide/styles/#expect http://chaijs.com/api/bdd/
const expect = require('chai').expect;
describe('Prime Factors calculator', function () {
it('returns the prime factors of a given integer', function () {
});
});
Run the test npm test or shorthand npm t
All pass as we don't have any assertions
Add our first test
expect(factorsOf(1)).to.eql([]);
Run the test npm test or shorthand npm t
It fails.
1) Prime Factors calculator returns the prime factors of a given in
teger:
ReferenceError: factorsOf is not defined
Add require for our implementation file.
const factorsOf = require('./factorsOf');
Run the test npm test or shorthand npm t
It fails.
Error: Cannot find module 'factorsOf'
Create empty implementation file
touch test/factorsOf.js Storing in the test directory for convenience.
Run the test npm test or shorthand npm t
It fails.
1) Prime Factors calculator returns the prime factors of a given in
teger:
TypeError: factorsOf is not a function
Add empty function to the implementation file
let factorsOf = _ => undefined;
Run the test npm test or shorthand npm t
It still fails - same error.
1) Prime Factors calculator returns the prime factors of a given in
teger:
TypeError: factorsOf is not a function
Export the function
module.exports = factorsOf;
Run the test npm test or shorthand npm t
It fails - but we now have the error we were expecting.
1) Prime Factors calculator returns the prime factors of a given in
teger:
AssertionError: expected undefined to deeply equal []
at Context.<anonymous> (test/factorsOf_test.js:6:29)
We can now start TDD
test for 1
expect(factorsOf(1)).to.eql([]);
solution (replace undefined with empty array)
let factorsOf = _ => [];
module.exports = factorsOf;
test for 2
expect(factorsOf(2)).to.eql([2]);
solution Try this but it fails first test. We need a condition here.
let factorsOf = _ => [2];
module.exports = factorsOf;
Lets refactor a bit....
Accept a parameter (n) declare a variable and initialize to empty array return the array At least we ar passing the first tests again.
let factorsOf = (n) => {
let factors = [];
return factors;
}
module.exports = factorsOf;
Lets add condition and push 2 onto the array
let factorsOf = (n) => {
let factors = [];
if (n > 1) {
factors.push(2);
}
return factors;
}
module.exports = factorsOf;
test for 3
expect(factorsOf(3)).to.eql([3]);
solution (Whats the absolute minimum keystrokes) change the constant 2 to variable n
let factorsOf = (n) => {
let factors = [];
if (n > 1) {
factors.push(n);
}
return factors;
}
module.exports = factorsOf;
test for 4
expect(factorsOf(4)).to.eql([2, 2]);
solution (we have nothing that will add two entries) add a check mod 2 and add 2 but fails first test
let factorsOf = (n) => {
let factors = [];
if (n > 1) {
if (n % 2 === 0) {
factors.push(2);
n /= 2;
}
factors.push(n);
}
return factors;
}
module.exports = factorsOf;
We need to surround factors.push(n); with a condition
Starting to sense a smell here
let factorsOf = (n) => {
let factors = [];
if (n > 1) {
if (n % 2 === 0) {
factors.push(2);
n /= 2;
}
if (n > 1) {
factors.push(n);
}
}
return factors;
}
module.exports = factorsOf;
test for 5, 6 and 7
expect(factorsOf(5)).to.eql([5]);
expect(factorsOf(6)).to.eql([2, 3]);
expect(factorsOf(7)).to.eql([7]);
solution (these work with solution for 4)
test for 8
expect(factorsOf(8)).to.eql([2, 2, 2]);
solution (change if to while)
let factorsOf = (n) => {
let factors = [];
if (n > 1) {
while (n % 2 === 0) {
factors.push(2);
n /= 2;
}
}
if (n > 1) {
factors.push(n);
}
return factors;
}
module.exports = factorsOf;
test for 9
expect(factorsOf(9)).to.eql([3, 3]);
solution (There is nothing that inserts a 3) We are really seeing a pattern here.
let factorsOf = (n) => {
let factors = [];
if (n > 1) {
while (n % 2 === 0) {
factors.push(2);
n /= 2;
}
if (n % 3 === 0) {
factors.push(3);
n /= 3;
}
}
if (n > 1) {
factors.push(n);
}
return factors;
}
module.exports = factorsOf;
test for 27
expect(factorsOf(27)).to.eql([3, 3, 3]);
solution (same as for 2, we see engine developing) Rules re being broken.
let factorsOf = (n) => {
let factors = [];
if (n > 1) {
while (n % 2 === 0) {
factors.push(2);
n /= 2;
}
while (n % 3 === 0) {
factors.push(3);
n /= 3;
}
}
if (n > 1) {
factors.push(n);
}
return factors;
}
module.exports = factorsOf;
Lets refactor
Add a divisor variable and initialize to 2
replace 2 with divisor in while loop
increment the divisor after the while
remove the while for 3
let factorsOf = (n) => {
let factors = [];
let divisor = 2;
if (n > 1) {
while (n % divisor === 0) {
factors.push(divisor);
n /= divisor;
}
divisor++;
}
if (n > 1) {
factors.push(n);
}
return factors;
}
module.exports = factorsOf;
we need to change the if to while
let factorsOf = (n) => {
let factors = [];
let divisor = 2;
while (n > 1) {
while (n % divisor === 0) {
factors.push(divisor);
n /= divisor;
}
divisor++;
}
if (n > 1) {
factors.push(n);
}
return factors;
}
module.exports = factorsOf;
no longer need that last if
let factorsOf = (n) => {
let factors = [];
let divisor = 2;
while (n > 1) {
while (n % divisor === 0) {
factors.push(divisor);
n /= divisor;
}
divisor++;
}
return factors;
}
module.exports = factorsOf;
I think that us done.
lets refactor first while to a for
let factorsOf = (n) => {
let factors = [];
for (let divisor = 2; n > 1; divisor++) {
while (n % divisor === 0) {
factors.push(divisor);
n /= divisor;
}
}
return factors;
}
module.exports = factorsOf;
lets refactor the other while to a for
let factorsOf = (n) => {
let factors = [];
for (let divisor = 2; n > 1; divisor++) {
for (; n % divisor === 0; n /= divisor) {
factors.push(divisor);
}
}
return factors;
}
module.exports = factorsOf;
Thanks us done.