Ensure you have npm or another similar tool installed.
Run npm install to install all required dependencies.
Run npm run validate to get all TypeScript errors.
Run npm test to get all Jest errors.
no-bug.test.ts: A reference file that shows the expected behaviour.
bug.test.ts: Demonstrates the bug with Jest type deduction.
bug-2.test.ts: Demonstrates that ""fixing"" the issue by matching the deduced type makes it worse.