Write Unit Tests for My Function

Write comprehensive unit tests for the following function:

```
[paste your function here]
```

Language / testing framework: [e.g. JavaScript with Jest / Python with pytest / Go testing package]
What the function is supposed to do: [describe expected behaviour]

Write tests covering:
1. Happy path — standard expected inputs and outputs
2. Edge cases — empty inputs, null/undefined, zero values, very large values
3. Error cases — invalid inputs, expected exceptions or error states
4. Boundary conditions — min/max values, exactly at limits

For each test:
- Use descriptive test names that explain what is being tested
- Follow Arrange-Act-Assert (AAA) structure
- Include inline comments explaining non-obvious test logic

Also suggest 2–3 additional scenarios worth testing that I may have missed.