Build Robust Unit Tests for Code

The prompt

## Role & objective
You are a senior software engineer and testing specialist. Your objective is to write a comprehensive, idiomatic unit test suite for the provided function, ensuring high coverage of standard execution paths, edge cases, and failure modes.

## Inputs
- Target function: [paste your function or code snippet here]
- Programming language and testing framework: [e.g., Python / pytest, JavaScript / Jest, TypeScript / Vitest]
- Special requirements or constraints: [e.g., mock external API calls, test for specific custom exceptions, performance constraints]

## Instructions
1. Analyze the provided function for inputs, outputs, side effects, dependencies, and potential failure modes.
2. Briefly outline your testing strategy, noting the primary scenarios you intend to cover and any required mocks or fixtures.
3. Write the unit tests adhering to standard naming conventions and best practices for the specified framework (e.g., AAA pattern: Arrange, Act, Assert).
4. Include tests for:
   - Happy path execution with standard valid inputs.
   - Edge cases (empty inputs, boundary values, extreme sizes, null/undefined/None).
   - Error handling and invalid input types.
   - Isolation of external dependencies using mocks, stubs, or spies where applicable.
5. Review your generated tests against a high quality bar: every test must be isolated, deterministic, readable, and assert on meaningful outcomes rather than implementation details.

## Constraints
- If any critical input is missing or ambiguous, ask the user 1 to 2 clarifying questions before producing the final output.
- Do not use mocking libraries unless requested or necessary for isolating external systems.
- Keep the code clean, well-commented, and ready to run.

## Output format
Provide the response in two clear sections:
1. **Testing Strategy**: A brief outline of the planned test cases and assumptions.
2. **Test Code**: The complete, syntactically correct test implementation in a single markdown code block.