Add unit tests

[bfonta]

As the project grows, we should add simple unit tests, to avoid constant bug fixes. As a start:

• check provide_* functions for event and geometry data
• run the reconstruction chain for multiple parameters and guarantee that it completes successfully and the final result makes sense
• run the validation of the reconstruction chain
• make sure the event display scripts complete successfully

The above should run automatically every time a PR is submitted for review.