piglop / timecop
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Description: A gem providing a unified method to mock Time.now, Date.today, and DateTime.now. It provides "time travel" capabilities, making it dead simple to test time-dependent code by either freezing or moving the concept of now.
Homepage: http://rubyforge.org/projects/johntrupiano/
Clone URL: git://github.com/piglop/timecop.git 
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Sat Oct 24 13:27:28 -0700 2009
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README.rdoc

timecop

DESCRIPTION

A gem providing "time travel" and "time freezing" capabilities, making it dead simple to test time-dependent code. It provides a unified method to mock Time.now, Date.today, and DateTime.now in a single call.

INSTALL

  gem install timecop

FEATURES

  • Freeze time to a specific point.
  • Travel back to a specific point in time, but allow time to continue moving forward from there.
  • No dependencies, can be used with any ruby project
  • Timecop api allows arguments to be passed into #freeze and #travel as one of the following:
    • Time instance
    • DateTime instance
    • Date instance
    • individual arguments (year, month, day, hour, minute, second)
    • a single integer argument that is interpreted as an offset in seconds from Time.now
  • Nested calls to Timecop#travel and Timecop#freeze are supported — each block will maintain its interpretation of now.

USAGE

Run a time-sensitive test 

  joe = User.find(1)
  joe.purchase_home()
  assert !joe.mortgage_due?
  # move ahead a month and assert that the mortgage is due
  Timecop.freeze(Date.today + 30) do
    assert joe.mortgage_due?
  end

Set the time for the test environment of a rails app — this is particularly helpful if your whole application is time-sensitive. It allows you to build your test data at a single point in time, and to move in/out of that time as appropriate (within your tests)

in config/environments/test.rb 

  config.after_initialize do
    # Set Time.now to September 1, 2008 10:05:00 AM (at this instant), but allow it to move forward
    t = Time.local(2008, 9, 1, 10, 5, 0)
    Timecop.travel(t)
  end

The difference between Timecop.freeze and Timecop.travel

#freeze is used to statically mock the concept of now. As your program executes, Time.now will not change unless you make subsequent calls into the Timecop API. #travel, on the other hand, computes an offset between what we currently think Time.now is (recall that we support nested traveling) and the time passed in. It uses this offset to simulate the passage of time. To demonstrate, consider the following code snippets: 

  new_time = Time.local(2008, 9, 1, 12, 0, 0)
  Timecop.freeze(new_time)
  sleep(10)
  new_time == Time.now # ==> true

  Timecop.return # "turn off" Timecop
  Timecop.travel(new_time)
  sleep(10)
  new_time == Time.now # ==> false

REFERENCES