add more tests, to get understanding of implemented features, e.g. builttin functions etc. #5
Description
motivation
there are quite some functions already built in - which is great ... but the tests do not cover them.
we should aim to test all builtin functions, to ease the documentation #4 as well.
Implementation hints:
- there are many tests to write ... consider making multiple small incremental PRs - not a single huge one
- using this the DMN Feel Handbook as inspiration to write more tests.