Introduce automated tests

[oehrlis]

Define and implement automated tests for tools. e.g. by using worklfows, containers etc.

[oehrlis]

some sources to consider:

• https://bach.sh/
• https://github.com/kward/shunit2
• https://github.com/bats-core/bats-core

[oehrlis]

add some basic scripts test_scripts.sh as well test_unit.sh