Simplified example of how rspec works

mini_rspec.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'colorize'
end

class MatcherInterface
  def initialize(some_object)
    @some_object = some_object
  end

  def to(matcher)
    if matcher.matches?(@some_object)
      puts "Test Passed".colorize(:green)
    else
      puts "Test Failed".colorize(:red)
    end
  end

  def not_to(matcher)
    if matcher.doesnt_match?(@some_object)
      puts "Test Passed".colorize(:green)
    else
      puts "Test Failed".colorize(:red)
    end
  end
end

class HaveValue
  def initialize(value)
    @value = value
  end

  def matches?(object)
    @value == object
  end

  def doesnt_match?(object)
    @value != object
  end
end

def expect(some_object)
  MatcherInterface.new(some_object)
end


def have_value(value)
  HaveValue.new(value)
end

foo = 1
expect(foo).to have_value(1)
expect(foo).not_to have_value(2)

bar = 100
expect(bar).to have_value(200)
expect(bar).not_to have_value(100)

Nice!

Very nice illustration