Unit Test Generator with Edge Cases

Write comprehensive unit tests for the following function using Vitest.

<span class="workshop-var-empty">{{code}}</span>

Generate tests covering:

1. Happy path — Normal, expected inputs and outputs
2. Edge cases — Empty inputs, single elements, maximum values, boundary conditions
3. Invalid inputs — Wrong types, null/undefined, malformed data
4. Error scenarios — What should throw or return error states
5. Concurrency/timing — If applicable, race conditions or async edge cases

For each test:

• Give it a descriptive name that explains what it verifies
• Include a brief comment on WHY this case matters
• Use arrange-act-assert pattern

After the tests, list any additional scenarios that would require integration tests rather than unit tests.