Unit Test Generator

Write a comprehensive unit test suite for the following [LANGUAGE] function/class using [TEST FRAMEWORK — Jest/Pytest/JUnit/etc.]. Code: [PASTE CODE HERE] Include tests for: (1) the happy path (expected inputs producing expected outputs), (2) edge cases (empty strings, null/undefined, zero, negative numbers, maximum values), (3) error cases (invalid inputs that should throw or return errors), (4) any async behavior if applicable. Use descriptive test names in the format 'should [expected behavior] when [condition]'. Add a brief comment explaining what each test group is validating. Aim for at least 90% branch coverage.