How can I test Perl applications using a changing system time?

Question

I have a web application that I want to run some system tests on, and in order to do that I'm going to need to move the system time around. The application used DateTime all the way through.

Has anyone got any recommendations for how to change the time that DateTime->now reports? The only thing that comes to mind is subclassing DateTime and messing about with all the 'use' lines, but this seems rather invasive.

Note on answers:

All three will work fine, but the Hook::LexWrap one is the one I've chosen because (a) I want to move the clock rather than jiggle it a bit (which is more the purpose of what Time::Mock and friends do); (b) I do, consistently, use DateTime, and I'm happy to have errors come out if I've accidentally not used it; and (c) Hook::LexWrap is simply more elegant than a hack in the symbol table, for all that it does the same thing. (Also, it turns out to be a dependency of some module I already installed, so I didn't even have to CPAN it...)

Answer 1

Rather than taking the high-level approach and wrapping DateTime specifically, you might want to look into the modules Test::MockTime and Time::Mock, which override the low-level functions that DateTime etc. make use of, and (with any luck) will do the right thing on any time-sensitive code. To me it seems like a more robust way to test.