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

You can use code injection via Hook::LexWrap to intercept the now() method.

use Hook::LexWrap;

use DateTime;

# Use real now
test();

{
    my $wrapper = wrap 'DateTime::now',
        post => sub {
            $_[-1] = DateTime->from_epoch( epoch => 0 );
        };

    # Use fake now
    test();

}

# use real now again
test();

sub test {
    my $now = DateTime->now;

    print "The time is $now\n";
}