Red-Green-Refactor by Example related exercise as part of the Fundamentals of TDD course in Upcase (https://thoughtbot.com/upcase/videos/red-green-refactor-by-example)

spec.rb

require 'rspec/autorun'

class Person

  def initialize(first_name: , middle_name: nil, last_name: )
    @first_name = first_name
    @middle_name = middle_name
    @last_name = last_name
  end

  def full_name
    [first_name, middle_name, last_name].compact.join(' ')
  end

  def full_name_with_middle_initial
    [first_name, middle_name ? middle_name[0] : nil, last_name].compact.join(' ')
  end

  def initials
    [first_name[0], middle_name ? middle_name[0] : nil, last_name[0]].compact.join(' ')
  end

  private

    attr_reader :first_name, :middle_name, :last_name
end

RSpec.describe Person do
  describe '#full_name' do
    it 'concatenates first name middle name and last name' do
      person = Person.new(first_name: 'Raj', middle_name: 'Aryan', last_name: 'Sharma')

      expect(person.full_name).to eq('Raj Aryan Sharma')
    end

    it "does not add extra spaces if middle name is missing" do
      person = Person.new(last_name: 'Sharma', first_name: 'Raj')

      expect(person.full_name).to eq('Raj Sharma')
    end
  end

  describe "#full_name_with_middle_initial" do
    it 'displays full name with middle initial' do
      person = Person.new(first_name: 'Raj', middle_name: 'Aryan', last_name: 'Sharma')

      expect(person.full_name_with_middle_initial).to eq('Raj A Sharma')
    end

    it 'displays full name with no middle initial if no middle name' do
      person = Person.new(first_name: 'Raj', last_name: 'Sharma')

      expect(person.full_name_with_middle_initial).to eq('Raj Sharma')
    end
  end

  describe "#initials" do
    it 'gets the initials with regard to a name' do
      person = Person.new(first_name: 'Raj', middle_name: 'Aryan', last_name: 'Sharma')

      expect(person.initials).to eq('R A S')
    end

    it 'middle name is missing. It gets the initials with regard to other parts of name' do
      person = Person.new(first_name: 'Raj', last_name: 'Sharma')

      expect(person.initials).to eq('R S')
    end
  end
end