author-regression-test

name	author-regression-test
description	Author a failing regression-test artifact (a YAML eval-spec with grep or structural assertions) that captures the defect from rca.yaml / design.yaml, verify it is in a red state against the current codebase, and return the path. Enforces the TDD red-before-green invariant for the fix-it play.
user-invocable	false
model	sonnet
allowed-tools	Read, Write, Grep, Glob, Bash

author-regression-test

Model-invocable skill for regression-test artifact authorship and red-state verification.

Purpose

Given a completed RCA and fix design, write a YAML eval-spec regression test that will PASS when the fix is applied and FAIL on the current (unfixed) codebase. Verify it fails before returning — if it passes on the unfixed code, the test is not a regression test and the skill fails.

This enforces the red-before-green invariant (C14 of /fix-it) without any builder self-report. tech-designer invokes this skill instead of writing the test file inline.

Input

Field	Required	Description
rca_path	yes	Path to rca.yaml
design_path	yes	Path to design.yaml
project_root	yes	Codebase root — assertions execute against this
test_style	optional	yaml_eval_spec (default for YAML/markdown-only repos) or unit_test (code repos with a test runner)
runner_hint	optional	Command hint for unit-test style (e.g., pytest path::test)
output_base	yes	Directory to write regression-test.yaml

Process

1. Read RCA + design. Identify the root cause's file + logic + why-wrong.

2. Derive an observable assertion. Choose an assertion that is:

   • Specific — asserts the fix was applied (e.g., "line X no longer contains Y", "function Z handles empty list")
   • Mechanical — runnable with grep/ripgrep, file existence, structural YAML/JSON checks, or a unit-test command
   • Red on current code — the assertion fails now, before the fix

3. Author regression-test.yaml:

   style: yaml_eval_spec | unit_test
   target_issue: "{issue_number}"
   based_on:
     rca: "{rca_path}"
     design: "{design_path}"
   assertions:
     - id: A1
       description: "{what this proves}"
       kind: grep_absent | grep_present | file_exists | file_shape | command_exit_zero
       spec:
         # for grep_absent / grep_present:
         pattern: "{regex}"
         path: "{file or glob}"
         # for file_exists:
         path: "{file}"
         # for command_exit_zero:
         command: "{shell}"
         cwd: 
    
    
    
    
   

Output

regression_test_path: "{output_base}/regression-test.yaml"
style: yaml_eval_spec | unit_test
assertion_count: {n}
red_verified: true
verified_at: "{ISO-8601}"
status: written

Failure Modes

What failed	Cause	Return
RCA or design missing	I/O	status: failed, reason: missing_input
Assertion already green on unfixed code	Test does not capture the defect	status: failed, reason: already_green, green_assertions
Assertion execution error	Malformed pattern/command	status: failed, reason: assertion_error, assertion_id, error
No observable assertion derivable	RCA too abstract	status: failed, reason: no_observable_assertion

Boundaries

• Read-only against codebase except for writing the test file into {output_base}.
• The test must be verified red before the file is written — never write an unverified test.
• You do not run the quality-auditor verification loop — that is the agent's job post-implement.
• You do not modify source code to make the test pass.