Time dependent unit tests

Joda time supports setting a "fake" current time through the setCurrentMillisFixed and setCurrentMillisOffset methods of the DateTimeUtils class.

See https://www.joda.org/joda-time/apidocs/org/joda/time/DateTimeUtils.html

Java 8 introduced the abstract class java.time.Clock which allows you to have an alternative implementation for testing. This is exactly what Jon suggested in his answer back then.

The best way (IMO) of making your code testable is to extract the dependency of "what's the current time" into its own interface, with an implementation which uses the current system time (used normally) and an implementation which lets you set the time, advance it as you want etc.

I've used this approach in various situations, and it's worked well. It's easy to set up - just create an interface (e.g. Clock) which has a single method to give you the current instant in whatever format you want (e.g. using Joda Time, or possibly a Date).