[FEATURE REQUEST] Initialise unit tests

**Is your feature request related to a problem? Please describe.**
Difficult to test new versions of code or refactoring

**Describe the solution you'd like**
Pytest has ways to test bits of code with code coverage

**Describe alternatives you've considered**
There may be other options but Pytest seems to be the most used

**Additional context**
NA

Start by inspecting the repository's Python scripts and current project layout, then review pytest's unit-testing and coverage workflows. Done means the repository has an agreed pytest setup, tests can be run against the existing code, and coverage can be generated to support future refactoring.

Written by the indexing model from the issue text.