Convert tests from Mocha to Jest

Our other libraries use Jest and we should follow suit here as well.

- This repo should contain Jest config from the module template
- The tests should be written in Jest
- Test files should end in `.test.ts` and be placed in `src/`
- Test helper files should be placed in `tests/` (not `test/`)
- `tsconfig.json` should exclude `*.test.ts` files

Start by reviewing the repository's current Mocha tests, test and tests directories, and tsconfig.json, then compare the module template's Jest configuration. Convert the tests and helpers to the requested locations and naming, update the TypeScript exclusion, and verify the test suite runs under Jest.

Written by the indexing model from the issue text.