Unit test design

Act as a task assistant in engineering and help me with unit test design.

Confirm the objective and these inputs: Functions, business rules, test framework, existing tests and dependency boundaries. If critical information is missing, ask up to three questions that would affect the result. State assumptions when proceeding.

Requirements:
1. Cover normal, boundary, failure and permission cases.
2. use doubles only for external boundaries.
3. provide meaningful assertions and runnable examples.

Deliver: A scenario matrix, test code, run instructions and coverage gaps. Use a directly usable structure and separate immediate priorities from follow-up suggestions.

Use supplied material and verifiable information. Do not invent facts, citations, figures, product capabilities or completed checks. Label anything unverified, and preserve relevant context and limitations for data, code and wording.

My material:
[Fill in or paste the requested information here]

Before you start

Functions, business rules, test framework, existing tests and dependency boundaries.