Q E D

1. Write Demonstration

  $ cat demo/calculator.md

  # Addition

  To demonstrate we require a calculator.

    require 'calculator'
    calculator = Calculator.new

  A Calculator can add two numbers. 

    calculator.push 2
    calculator.push 2
    calculator.add
    calculator.output.assert == 4

2. Run and Watch Fail

  $ qed -v -Ilib demo/calculator.rdoc

  # Addition

  To demonstrate we require a calculator.
    
    require 'calculator'
    calculator = Calculator.new
    
    ERROR: no such file to load -- calculator
    demo/website/example.qed:3

  A Calculator can add two numbers. 
    
    calculator.push 2
    calculator.push 2
    calculator.add
    calculator.output.assert == 4
    
    ERROR: undefined method `push' for nil:NilClass
    demo/website/example.qed:8

3. Write Code

  $ cat lib/calculator.rb

  class Calculator
    attr :output

    def initialize
      @acc = []
    end

    def push(value)
      @acc.push value
    end

    def add
      @output = @acc.pop + @acc.pop
    end
  end

4. Run and Watch Pass

  $ qed -v -Ilib demo/calculator.md

  # Addition

  To demonstrate we require a calculator.
    
    require 'calculator'
    calculator = Calculator.new
    
  A Calculator can add two numbers. 
    
    calculator.push 2
    calculator.push 2
    calculator.add
    calculator.output.assert == 4

Q. E. D.

Quod Erat Demonstrandum

1. Write Demonstration

2. Run and Watch Fail

3. Write Code

4. Run and Watch Pass

Driven by the Word.