Add unit tests with 90%+ coverage

[esr360]

As a user of Lucid, I want to be able to run unit tests against the library, in order to determine the reliability of the code and have more confidence when using it.

Acceptance criteria:

• Test coverage is handled by https://codecov.io, and available via https://codecov.io/gh/One-Nexus/Lucid
• Codecov reports coverage of 90% or greater