Unit Test Writer

Write unit tests for the following function or module.

Language: [language] Testing framework: [testing_framework] Function / module name: [function_name] What it does: [function_description]

Code to test:

[code]

Write tests covering:

1. Normal / happy path (at least 2 cases)
2. Edge cases: [edge_cases]
3. Invalid inputs and error conditions
4. Boundary values

Follow [testing_framework] conventions. Include descriptive test names and arrange-act-assert structure.