Part eight of a series of posts about automated testing.

How does Santa deliver presents to all the millions of children on Christmas Eve? Simple, just stop time! But how do we test that?

Here’s one way to do it in Perl:

use Test::MockTime qw( :all );

my $santa;

sub setup : Test(setup) {
$santa = Santa->new();
}

# FIXME: these tests are specific to GMT
sub santa_should_not_deliver_presents_before_midnight : Test {
set_absolute_time('2017-12-24T23:59:59Z');
is($santa->has_delivered_presents(), 0);
}

sub santa_should_have_delivered_all_presents_after_midnight : Test {
set_absolute_time('2017-12-25T00:00:01Z');
is($santa->has_delivered_presents(), 1);
}

By messing with the clock, we can quickly test all sorts of time-dependent code, without having to call sleep() and slowing down the tests.

Further reading