Add unit tests for lua backends

Summary: According T3872, I have added some simple unit tests for lua backend, checking results with `lua`. The tests coverage some most common use. But not all tests pass completely: some tests skipped because of problems with the lua backend.

Test Plan: 1) run `testlua`

Reviewers: #cantor, asemke

Reviewed By: #cantor, asemke

Subscribers: asemke, filipesaraiva, #cantor, #kde_edu

Tags: #kde_edu, #cantor

Differential Revision: https://phabricator.kde.org/D11791