#98 Use demos as regression tests

[Ulf Lorenz]

By now, we have assembled a few demos that showcase Wavepacket's capabilities. In principle, these should be extended such that all usual use-cases are covered. Hence, they could also double as regression tests to make sure all use-cases still work as expected.

This task is about using CTest (the testing tool of cmake) to turn the demos into regression tests. It should be possible to run all demos and compare their output against a reference output (stored in the git repository). Having them run through would then become part of the merge into the master branch.

Along the way, also ponder if the demos make obsolete the acceptance tests. If so, the acceptance tests could simply be dropped or converted into demos where sensible.

---

kept the acceptance tests for now. Little harm in them. Defered some luxury problems to [#119].