Freezing Time

When dealing with an HTTP API that includes time-based compontents in the request (e.g. for signed S3 requests), it can be useful on playback to freeze time to what it originally was when the cassette was recorded so that the request is always the same each time your test is run.

While VCR doesn't directly support time freezing, it does expose VCR::Cassette#originally_recorded_at, which you can easily use with a library like timecop to freeze time.

Note: VCR::Cassette#originally_recorded_at will return nil when the cassette is recording for the first time, so you'll probably want to use an expression like cassette.originally_recorded_at || Time.now so that it will work when recording or when playing back.

Previously recorded responses are replayed

Given a previously recorded cassette file "cassettes/example.yml" with:

--- 
http_interactions: 
- request: 
    method: get
    uri: http://example.com/events/since/2013-09-23T17:00:30Z
    body: 
      encoding: UTF-8
      string: ""
    headers: {}
  response: 
    status: 
      code: 200
      message: OK
    headers: 
      Content-Length: 
      - "20"
    body: 
      encoding: UTF-8
      string: Some Event
    http_version: "1.1"
  recorded_at: Mon, 23 Sep 2013 17:00:30 GMT
recorded_with: VCR 2.0.0

Given a file named "freeze_time.rb" with:

require 'time'
require 'timecop'
require 'vcr'

VCR.configure do |vcr|
  vcr.cassette_library_dir = 'cassettes'
  vcr.hook_into :webmock
end

VCR.use_cassette('example') do |cassette|
  Timecop.freeze(cassette.originally_recorded_at || Time.now) do
    path = "/events/since/#{Time.now.getutc.iso8601}"
    response = Net::HTTP.get_response('example.com', path)
    puts "Response: #{response.body}"
  end
end

When I run ruby freeze_time.rb

Then it should pass with "Response: Some Event".