Rspec functioning principle

spec.rb

# Core
class Object
  def should(matcher)
    puts matcher.match(self)
  end
end

class Matcher
  def initialize(expected, &block)
    @expected = expected
    @matcher  = block
  end

  def match(value)
    @matcher.call(@expected, value)
  end
end

# Matchers
def eq(value)
  Matcher.new(value) do |expected, given|
    if expected != given
      <<-EOF
        expected: #{expected}
        got:      #{given}
      EOF
    else
      "Equal"
    end
  end
end

def not_eq(value)
  Matcher.new(value) do |expected, given|
    if expected != given
      "Not equal"
    else
      <<-EOF
        expected not: #{expected}
        got:          #{given}
      EOF
    end
  end
end

def contains(value)
  Matcher.new(value) do |expected, given|
    if given.include?(expected)
      "Includes"
    else
      <<-EOF
        #{given} not contains #{expected}
      EOF
    end
  end
end

# Test
'hello'.should(eq('world'))
2.should eq(2)

(2).should not_eq(2)
(2 * 2).should not_eq(5)

[1, 2, 3].should contains(4)