be_close_to.rb

# Useful matcher for matching proximity of numbers so you can do things like
# 4.should be_close_to(5).by(1)
# or with Rails
# something.created_at.should be_close_to(somethingelse.created_at).by(10.minutes)
# "by" is not mandatory, but desirable since proximity is highly contextual

module CustomMatchers
  class BeCloseTo
    def initialize expected
      @expected = expected
      @tolerance = 40
    end
    
    def matches? actual
      @actual = actual
      @actual >= (@expected - @tolerance) and @actual <= (@expected + @tolerance)
    end
    
    def by tolerance
      @tolerance = tolerance
      self
    end
    
    def failure_message_for_should
      "expected #{@actual.inspect} to be close to #{@expected.inspect} by #{@tolerance}"
    end
    
    def failure_message_for_should_not
      "expected #{@actual.inspect} not to be close to #{@expected.inspect} by #{@tolerance}"
    end
  end
  
  def be_close_to expected
    BeCloseTo.new expected
  end  
end