How to fake Time.now?

Question

What\'s the best way to set Time.now for the purpose of testing time-sensitive methods in a unit test?

Answer 1

This kind of works and allows for nesting:

class Time
  class << self
    attr_accessor :stack, :depth
  end

  def self.warp(time)

    Time.stack ||= [] 
    Time.depth ||= -1 
    Time.depth += 1
    Time.stack.push time

    if Time.depth == 0 
      class << self    
          alias_method :real_now, :now  
          alias_method :real_new, :new

          define_method :now do
            stack[depth] 
          end

          define_method :new do 
            now 
          end
      end 
    end 

    yield

    Time.depth -= 1
    Time.stack.pop 

    class << self 
      if Time.depth < 0 
        alias_method :new, :real_new
        alias_method :now, :real_now
        remove_method :real_new
        remove_method :real_now 
      end
    end

  end
end

It could be slightly improved by undefing the stack and depth accessors at the end

Usage:

time1 = 2.days.ago
time2 = 5.months.ago
Time.warp(time1) do 

  Time.real_now.should_not == Time.now

  Time.now.should == time1 
  Time.warp(time2) do 
    Time.now.should == time2
  end 
  Time.now.should == time1
end

Time.now.should_not == time1 
Time.now.should_not be_nil