TDD: Clean Code That Works

Test Drive

Kaprekar Number

Kaprekar number is a non-negative integer, the representation of whose square can be split into two parts that add up to the original number.

Write a function that determines if a given number is a Kaprekar number or not.

Questions?

Predicted Questions

Can you explain what is Kaprekar number again, in an easily understandable language please?
Can you give me an example of its input?
What kind of output do you want me to print? Is it "true" or "false" value? Or is it "kaprekar" or "not kaprekar" value?

With No Tests

def kaprekar?(k)
  result = false
  power = k ** 2
  power_str = power.to_s
  for i in 0..(power_str.size - 1)
    num1 = power_str[0,i].to_i
    num2 = power_str[i,power_str.size-1].to_i
    if k == num1 + num2
      result = true
      break
    end
  end
  result
end

puts "Is kaprekar 9: #{kaprekar?(9)}"
puts "Is kaprekar 45: #{kaprekar?(45)}"
puts "Is kaprekar 7777: #{kaprekar?(7777)}"
puts "Is kaprekar -9: #{kaprekar?(-9)}"
puts "Is kaprekar 33: #{kaprekar?(33)}"

Self-Testing Code

What is Self-Testing Code?

Code that have built-in tests
which serve as a binding contract
and can be run arbitrarily

Install RSpec

source 'https://rubygems.org'

gem 'rspec'

Gemfile

bundle install

Execute command:

Change Directory Structure

.
├── Gemfile
├── Gemfile.lock
├── lib
│   └── kaprekar.rb
└── spec

Setup your directory structure to look like this:

Create Unit Tests

require "kaprekar"

describe 'Kaprekar' do
  it 'should return true when the input is 9 because 9 * 9 is 81 and 8 + 1 is 9' do
    expect(kaprekar?(9)).to eq(true)
  end

  it 'should return false when the input is 8 because 8 * 8 is 64 and 6 + 4 is not 8' do
    expect(kaprekar?(8)).to eq(false)
  end

  it 'should return false when the input is a negative integer' do
    expect(kaprekar?(-9)).to eq(false)
  end
end

spec/kaprekar_spec.rb

rspec -fd

Run:

The Parallels (1)

Remember the points in our questions earlier?

easily understandable
example input
expected output

The Parallels (2)

require "kaprekar"

describe 'Kaprekar' do
  it 'should return true when the input is 9 because 9 * 9 is 81 and 8 + 1 is 9' do
    expect(kaprekar?(9)).to eq(true)
  end

  it 'should return false when the input is 8 because 8 * 8 is 64 and 6 + 4 is not 8' do
    expect(kaprekar?(8)).to eq(false)
  end

  it 'should return false when the input is a negative integer' do
    expect(kaprekar?(-9)).to eq(false)
  end
end

easily understandable description

example input

expected output

Test Driven Development

The goal of test driven development is to produce clean code that works

- Ron Jeffries, founders of Extreme Programming

Steps

Write a test
Run the test and see it fails
Write just enough code to make it pass
Run the test and see it passes
Refactor
Run the test to ensure it still passes

FIRST Principle

Fast
Independent
Repeatable
Self-checking
Timely

But How? And Why?

Throughout the day, we are going to teach you how to write clean code that works while discovering why it matters.

Preparation

Non-Negotiable Ettiquette

Indentation and spacing between code constructs (classes/methods/specs) must be consistent
Use only spaces (no tabs) for indentation
Follow accepted naming conventions for Ruby
Follow accepted naming file and directory structure for Ruby
Use namespaces
No comments/unused code must ever be checked in
Use .gitignore
Ensure there is a README.md that includes
- Problem Description
- Dev environment setup
- Build instructions
- Run instructions
TDD (this should show in clear pattern in the commit log)

rm -rf

Failure to comply with non-negotiable etiquette will result in rm -rf to your code.

Group Responsibility

Ensure conventions
- indentation and spaces
- naming
- file and directory structure
Write a script that automate project structure to follow the conventions

Problem Sets

Problem Set #1

As a fan of geometry,
I want to model a line based on points consisting of (x, y) co-ordinates using the cartesian system,
So that I can calculate its length.

Problem Set #2

As a fan of geometry,
I want to compare two lines for equality based on the end points,
So that I know when two lines are the equal.

Problem Set #3

As a fan of geometry,
I want to model a rectangle with sides of lengths a and b,
So that I can calculate its perimeter.

Lessons Learned

Concepts

Express intent
Simple English modeling
Baby steps
YAGNI
DRY
KISS
SRP
- Job of class
- Tell, don't ask
- Law of Demeter

Clean code is not written by following a set of rules. You don’t become a software craftsman by learning a list of heuristics. Professionalism and craftsmanship come from values that drive disciplines.

TDD: Clean Code That Works

Test Drive

Kaprekar Number

Questions?

Predicted Questions

With No Tests

Self-Testing Code

What is Self-Testing Code?

Install RSpec

Change Directory Structure

Create Unit Tests

The Parallels (1)

The Parallels (2)

Test Driven Development

The goal of test driven development is to produce clean code that works

Steps

FIRST Principle

But How? And Why?

Preparation

Non-Negotiable Ettiquette

rm -rf

Group Responsibility

Problem Sets

Problem Set #1

Problem Set #2

Problem Set #3

Lessons Learned

Concepts

Clean code is not written by following a set of rules. You don’t become a software craftsman by learning a list of heuristics. Professionalism and craftsmanship come from values that drive disciplines.

TDD: Clean Code That Works

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