If you don't know anything about automated testing in Perl then you should
probably read about Test::Simple and Test::More before preceding.
Test::Deep uses the Test::Builder framework.
Test::Deep gives you very flexible ways to check that the result you got
is the result you were expecting. At it's simplest it compares two
structures by going through each level, ensuring that the values match,
that arrays and hashes have the same elements and that references are
blessed into the correct class. It also handles circular data structures
without getting caught in an infinite loop.