Before I started with perl I had a small intermezzo with Eiffel. In that fine programming language "design by contract" is one of the design philosophies. The "contracts" are assertions as described by ady, with the nice addition that assertions on methods are actually inherited.

So I miss assertions in perl a bit, but I am too lazy (and too concerned with not introducing dependencies) to use some dedicated modules for it.

My current usage of assertions is mostly limited to

use Carp qw(confess);
...
confess "assertion description" unless $condition
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It's a bit sad that Devel::Cover "punishes" the usage of assertions by default if you find no way to trigger it (and unless you tell Devel::Cover to ignore that line, which could also do).

So to me it seems that all the tools are in place, but either aren't easy accessible, or (more likely) I'm too lazy to use them properly.