Manage current time in unit testing?

Question

Is there a way to manipulate the current time in a jUnit 4.5 test? I have the following method that I would like to have unit test for

public String getLastWeek() { GregorianCalendar c = new GregorianCalendar(TimeZone.getTimeZone("Europe/Stockholm")); c.setFirstDayOfWeek(GregorianCalendar.MONDAY); c.add(GregorianCalendar.WEEK_OF_YEAR, -1); return c.get(GregorianCalendar.YEAR) + " " + c.get(GregorianCalendar.WEEK_OF_YEAR); } 

One way to simplify testing is to break it into two methods.

 public String getLastWeek() { GregorianCalendar c = new GregorianCalendar(TimeZone.getTimeZone("Europe/Stockholm")); return getLastWeekFor(c); } public String getLastWeekFor(GregorianCalander c) { c.setFirstDayOfWeek(GregorianCalendar.MONDAY); c.add(GregorianCalendar.WEEK_OF_YEAR, -1); return c.get(GregorianCalendar.YEAR) + " " + c.get(GregorianCalendar.WEEK_OF_YEAR); } 

This allows me to check the week subtraction logic, but leaves getLastWeek untested, and I prefer to have only one method for this.

Answer 1

You have no real way to manage your system time.

Actually, you reorganized the method pretty nicely to make it verifiable. I would keep it at the same time.

Answer 2

Here I see two ways.

Create a DateUtils factory class that encapsulates the construction of Calendar and Date instances. Then you can change it to a managed factory. Ie, you have a second DateUtils implementation that also provides the setCurrentTime method, and then explicitly returns the Calendar instances set for that date.

Or you can use JMockit to actually “override” your call to new GregorianCalendar , an mock instance is returned instead. I did not do this myself, but there is a description here .

Your option, splitting the method into two methods, is also a perfectly valid option. I think this is what most people, including myself, do, but it actually harms your design, especially if the class is exposed to different code.

Answer 3

Looks like you're trying to recreate what JODA Time is. I will bring it if you do not know. You can compromise between rethinking the wheel and adding a dependency.