When designing test cases, what is generally considered the best way to write high quality test cases so that they are clear, maintainable and useful over time?

Introduction / Context:
Good test cases are the foundation of effective and maintainable testing. This question asks about the best general approach to writing them. Interviewers want to see whether candidates value clarity, traceability and structure, which are essential when test suites grow large and multiple testers work on the same project over time.

Given Data / Assumptions:
- Test cases will be used by more than one tester or team over the life of the project.
- Requirements may change, and defects discovered in production may lead to new tests.
- The organisation may use manual or automated execution based on the same logical test cases.
- The aim is to define best practice rather than one specific template.

Concept / Approach:
High quality test cases share common features. They have unique identifiers and meaningful titles, which allow easy reference and reporting. They are traceable back to specific requirements or user stories, supporting coverage analysis. Each test case defines preconditions and initial data, clear step by step actions, expected results for each main step and final postconditions. The language is unambiguous so that different testers executing the same test obtain consistent behaviour. Good test cases are also maintainable, meaning they can be updated when requirements evolve.

Step-by-Step Solution:
Step 1: Identify which option mentions clarity, structure and traceability. Step 2: Option a includes uniquely identifiable cases, linkage to requirements and well defined preconditions, steps and expected results. Step 3: Confirm that this matches standard recommendations in testing literature. Step 4: Review other options to see whether they introduce vagueness or poor maintainability. Step 5: Decide that option a is the correct best practice description.

Verification / Alternative check:
To verify, imagine handing your test suite to a new team member. If test cases follow the structure in option a, the new tester can understand, execute and update them with minimal guidance. If they followed the other options, confusion and miscommunication would quickly appear. This experience based check confirms that option a is the best answer.

Why Other Options Are Wrong:
Option b promotes vague one line descriptions, which make it impossible to know the exact expected behaviour and reduce repeatability. Option c suggests combining many unrelated checks into one case, which makes debugging failures difficult. Option d discourages updates, which is dangerous in dynamic projects where change is inevitable.

Common Pitfalls:
Common pitfalls include writing overly detailed test cases that duplicate many small variations instead of using data driven approaches, or writing overly brief cases that leave out expected results. Another issue is failing to keep test cases aligned with evolving requirements, leading to outdated suites that no longer reflect the system. By following the best practices summarised in option a, teams can avoid many of these problems.

Final Answer:
Write test cases that are clear, uniquely identifiable and traceable to requirements, with well defined preconditions, steps, input data, expected results and postconditions so that any tester can execute them consistently.