Ruby: Time::is

Mocha is fantastic for unit testing, but I usually try to avoid requiring it while functional testing. In general this works, but Time.now is something that I occasionally like to fix even while functional testing. To solve the problem, within a functional test helper I load a time_extensions.rb file that defines a Time::is method. The Time::is method is useful for freezing time at a certain point and executing a block of code. When the block of code finishes the Time.now method is returned to it's original implementation.

The example below is how I usually solve the described problem.

require 'time'

class Time
  def self.metaclass
    class << self; self; end
  end
  
  def self.is(point_in_time)
    new_time = case point_in_time
      when String then Time.parse(point_in_time)
      when Time then point_in_time
      else raise ArgumentError.new("argument should be a string or time instance")
    end
    class << self
      alias old_now now
    end
    metaclass.class_eval do
      define_method :now do
        new_time
      end
    end
    yield
    class << self
      alias now old_now
      undef old_now
    end
  end
end

Time.is(Time.now) do
  Time.now # => Tue Nov 13 19:31:46 -0500 2007
  sleep 2
  Time.now # => Tue Nov 13 19:31:46 -0500 2007
end

Time.is("10/05/2006") do
  Time.now # => Thu Oct 05 00:00:00 -0400 2006
  sleep 2
  Time.now # => Thu Oct 05 00:00:00 -0400 2006
end