Test Case Writer Skill

Good test cases are unambiguous and complete: anyone can run them and get the same result, and together they cover the ways the feature can succeed and fail. This skill derives test cases from a requirement or user story — happy path first, then the edge and negative cases that find real bugs — each written so it's directly executable.

Working from a brief

Given a user story or a one-line feature description, write the test cases anyway — infer the acceptance criteria, boundaries, and likely failure modes, labelling assumptions. Always include edge and negative cases, not just the happy path. Never hand back questions instead of cases.

Required Inputs

Ask for these only if they aren't already provided (else infer and label):

• The requirement — the feature/user story and its acceptance criteria.
• Inputs & rules — fields, valid/invalid values, limits, and business rules that define correct behaviour.
• Scope & environment — UI/API/both, platforms, and any preconditions (logged-in, data state).
• Priority — what matters most (critical paths), so cases can be ordered.

Output Format

Test Cases: feature]

A short intro line, then cases in a table (or per-case blocks for complex flows):

| ID | Title | Type | Preconditions | Steps | Test data | Expected result | Priority | |---|---|---|---|---|---|---|---| | TC-01 | Valid login | Happy path | user exists | 1. … 2. … | valid creds | logged in, lands on … | High | | TC-02 | Wrong password | Negative | user exists | … | bad password | error shown, not logged in | High | | TC-03 | Empty fields | Negative/validation | — | … | blank | inline validation | Med | | TC-04 | Max-length input | Edge/boundary | — | … | boundary value | accepted/handled | Med |

Cover, deliberately: happy path, boundary/edge (empty, max, min, just over/under limits), negative (invalid input, wrong state, unauthorised), and any business-rule cases.

End with a coverage note: which acceptance criteria/requirements each case maps to, and any gaps or risks to flag for review.

Quality Checks

• ] Each case has clear preconditions, numbered steps, the test data, and a single expected result
• ] Steps are unambiguous — two testers would execute them identically
• ] Coverage includes edge/boundary and negative cases, not just the happy path
• ] Cases trace back to the acceptance criteria / requirement (coverage note)
• ] Cases are prioritised so the critical paths are obvious
• ] Expected results are specific and verifiable (not "works correctly")

Anti-Patterns

• ] Do not write only happy-path cases — the bugs live in the edges and negatives
• ] Do not write vague steps ("test the login") — give the exact actions and data
• ] Do not use unverifiable expected results ("it should work") — state the observable outcome
• ] Do not combine many checks into one bloated case — keep cases atomic and traceable
• ] Do not skip preconditions/test data — they're why a case is reproducible

Based On

Test-design practice — requirement-derived cases with boundary-value and negative testing, atomic executable steps, and traceability to acceptance criteria.