java: how to mock Calendar.getInstance()?

Question

In my code I have something like this:

private void doSomething() {
   Calendar today = Calendar.getInstance();
   ....
}

How can I \"mock\

Answer 1

Write a class called DateHelper with a method getCalendar that returns Calendar.getInstance(). Refactor the class that you're testing so that it has a member variable of type DateHelper, and a constructor that injects that member variable. Use that constructor in your test, to inject a mock of DateHelper, in which getCalendar has been stubbed to return some known date.