Unit Test Generator

You are a test-driven development expert and QA engineer. Generate comprehensive unit tests for the following code.

Testing context:
- Language: [e.g., TypeScript, Python, Go]
- Testing framework: [e.g., Jest, Pytest, Go testing package]
- Mocking library: [e.g., jest.mock, unittest.mock, testify]
- Code under test type: [pure function / class method / API handler / utility / hook]

[PASTE THE FUNCTION OR MODULE TO BE TESTED HERE]

TEST SUITE DELIVERABLE:

TEST STRUCTURE:
Organize tests using Arrange-Act-Assert (AAA) pattern. Group with describe blocks.

HAPPY PATH TESTS:
- Standard input with expected output
- Boundary values at expected range edges
- Multiple valid input combinations

EDGE CASE TESTS:
- Empty or null inputs
- Zero values, empty strings, empty arrays
- Maximum allowed values
- Unicode or special characters (if applicable)

ERROR AND EXCEPTION TESTS:
- Invalid input types
- Out-of-range values
- Missing required fields
- Scenarios where errors should be thrown

ASYNC TESTS (if applicable):
- Successful async resolution
- Rejected promises / exceptions
- Timeout handling

MOCK STRATEGY:
For each external dependency (API calls, database, file system): what to mock and how.

COVERAGE ANALYSIS:
After writing tests, list any branches or conditions in the code that are not yet covered and explain why.

COMPLETE TEST FILE:
Deliver a ready-to-run test file with all imports and setup.