Description:

Tainted data is data that comes from an unsafe source, such as the
command line, or, in the case of web apps, any GET or POST
transactions (see perlsec(1) man page for details on why tainted data
is bad, and how to untaint the data).

When you're writing unit tests for code that deals with tainted data,
you'll want to have a way to provide tainted data for your routines to
handle, and easy ways to check and report on the taintedness of your
data, in standard Test::More style.