Add type checking and linting for tests

### Is your feature request related to a problem? Type checking and linting are currently disabled for tests. When migrating to ESLint 9 in https://github.com/github-community-projects/private-mirrors/pull/409, this led to issues until tests were excluded ### Describe the solution you'd like 1. Add tests to TSConfig, instead of excluding them, and fix type checking issues 2. Add tests to ESLint config, instead of excluding them, and fix linting issues ### Describe alternatives you've considered Leave tests excluded and risk bugs or issues not caught by type checking or linting. ### Additional context _No response_