josephwilk/fake_execution

module FakeExecution
  def self.activate!
    Kernel.class_eval do
      alias_method :real_system, :system
      alias_method :system, :fake_system

      alias_method :real_exec, :exec
      alias_method :exec, :fake_exec

      alias_method :real_backtick, :`
      alias_method :`, :fake_backtick
    end
    true
  end

  def self.deactivate!
    Kernel.class_eval do
      # Have we been activated?
      if method_defined?(:real_backtick)
        alias_method :fake_backtick, :`
        alias_method :`, :real_backtick

        alias_method :fake_system, :system
        alias_method :system, :real_system

        alias_method :fake_exec, :exec
        alias_method :exec, :real_exec
      end
    end    
    true
  end
end

def FakeExecution
  return ::FakeExecution unless block_given?
  ::FakeExecution.activate!
  yield
ensure
::FakeExecution.deactivate!
end