Clojure: Freezing Time Added To Expectations

If you're using expectations and Joda Time, you now have the ability to freeze time in bare expectations (version 1.4.16 and above). The following code demonstrates how you can use the freeze-time macro to set the time, verify anything you need, and allow time to be reset for you.

(ns blog-expectations
  (:use expectations)
  (:import [org.joda.time DateTime]))

(defn add-timestamp [m]
  (assoc m :time (DateTime.)))

(expect {:time (DateTime. 1)}
        (freeze-time (DateTime. 1)
                     (add-timestamp {})))

Under the covers freeze-time is setting the current millis using the DateTime you specify, running your code and resetting the current millis in a finally. As a result, after your code finishes executing, even if finishing involves throwing an exception, the millis of Joda Time will be set back to working as you'd expect.

The freeze-time macro can be used in both the expected and actual forms, and can be nested if you need to set the time multiple times within a single expectation.