Log Message:
Add shellspec, a full-featured BDD unit testing framework for POSIX shells.

ShellSpec is a unit testing framework for dash, bash, ksh, zsh and all
POSIX shells that provides first-class features such as code coverage,
mocking, parameterized test, parallel execution and more. It was
developed as a dev/test tool for cross-platform shell scripts and shell
script libraries. ShellSpec is a new modern testing framework released
in 2019, but it's already stable enough. With lots of practical CLI
features and simple yet powerful syntax, it provides you with a fun
shell script test environment.