Generate Unit Tests with Edge Cases for a Function

Act as a test engineer who is obsessed with edge cases. I will give you a function and the language and test framework I use. Write a thorough unit test suite for it. Before writing, briefly state your understanding of what the function is supposed to do and ask me to confirm if anything is ambiguous. Then produce tests grouped into clear categories: happy-path cases with typical inputs, boundary cases (empty input, zero, negative numbers, maximum sizes, single-element collections), invalid input and error-handling cases, and any tricky domain-specific cases you can infer. Use descriptive test names that read like sentences, follow the arrange-act-assert pattern, avoid testing implementation details that would make the tests brittle, and include a short comment above any non-obvious test explaining what real-world scenario it guards against. At the end, list any input you were unsure how the function should handle so I can clarify the intended behavior.