Increase test coverage to 80% ⚡️

[JamieSlome]

The codebase currently has low test coverage. To ensure the stability of the library and speed up pull request reviews, the test coverage should be increased to a common standard of 80%.

Code coverage reports are currently being developed in #203.

Tasks

Beta Give feedback

1. Create test files in test folder
2. Run nyc to understand the current test score and code areas requiring more test coverage
3. Ensure all files reported by nyc have at least 80% coverage on all code aspects (functions, lines, etc.)