Tidy up unittests

[CasperWA]

PR #208 moved to proper pytest functions for the tests, however, it didn't tidy up the tests.

The tests should be revisited and considered whether they can be optimized.

Most importantly, the tests shouldn't produce a lot of "garbage" files; all files should be temporary if at all.
For examples one can/should add these to the examples/ folder or demo/.