Unit test

I added some dummy unit tests plus a coverage report.

the 'jest' test framework requires some funky business when pulling in external dependencies like svg.js, which I haven't gotten my head around yet, so the tests here are functionally useless but are at least a stopping point.

Additionally, added a 'unit' section to the test step in the pipeline. Will have to go back and clean things up, but am learning tonnes about how we can best structure our individual functional units so they are robust.