TestML is a generic, programming language agnostic, meta language for
writing unit tests. The idea is that you can use the same test files in
multiple implementations of a given programming idea. Then you can be more
certain that your application written in, say, Python matches your Perl
implementation.

In a nutshell you write a bunch of data tests that have inputs and expected
results. Using a simple syntax, you specify what functions the data must
pass through to produce the expected results. You use a bridge class to
write the data transform functions that pass the data through your
application.

In Perl 5, TestML is the evolution of the the Test::Base manpage module. It
has a superset of Test:Base's goals. The data markup syntax is currently
exactly the same as Test::Base.