Add basic tests and examples

[eirikurj]

Purpose

This PR adds basic tests for CLI scripts and simple python scripts showing direct usages.

At this stage I only added a couple of examples, but all examples are tested. Currently, the output is not directly checked. Ideally, both the CLI and module outputs should be tested. Before proceeding, it would be good to get feedback on the level of tests we should add. For example, for output, we could store reference BDFs, use the BaseRegTest or add ref data directly to tests. Let me know what you feel is the most appropriate.

Expected time until merged

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

Checklist

• I have run flake8 and black to make sure the Python code adheres to PEP-8 and is consistently formatted
• I have formatted the Fortran code with fprettify or C/C++ code with clang-format as applicable
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation