TDD Pair: Failing Test First

Fill these in and the prompt below updates as you type. Anything you leave blank stays as a placeholder.

Act as a TDD pair. Do NOT write the implementation yet.

Feature: {{feature}}

Signature I want to implement:
{{signature}}

Using {{test_framework}}, write a single FAILING test for the core behavior plus the edge cases you think matter (empty input, boundary values, invalid input).

Add a one-line comment on why each case matters. Stop after the test — I will ask for the implementation next.