I Built a Claude Code Skill That Finds Broken Callers Before You Deploy

A developer built Test Shield, a tool that detects broken callers before deployment by tracing which callers depend on changed functions. The tool was created after a bug fix in a Chinese chess app silently broke two callers, causing production issues despite 87% test coverage. Test Shield uses AST static analysis to identify impacted callers and generate regression tests, with an honesty report for dynamic call blind spots.

You fix a bug. You deploy. Three hours later, production is on fire. Here's how I built a tool to stop that. I was working on a Chinese chess app. Changed is checkmate — added a simple empty-board guard clause. Two lines. Trivial. Ran my tests. Green. Deployed. Two hours later: puzzle solving was broken. Level submission returned wrong results. I changed one function. It silently broke two callers I didn't even know existed. The test coverage report said 87%. It didn't matter. Coverage tells you which lines ran — not which callers your change silently corrupted. Test Shield — a Claude Code skill with one job: /test-shield │ ▼ Changed: is checkmate — chess utils.py:320 ⚠️ Unexpected impact: ● solve puzzle — levels.py:687 ← wouldn't have caught this ● submit level solution — levels.py:516 ← or this → Generate 6 regression tests → 4/6 pass, 2 need review → Safe to merge. Here's the evidence. Coverage tells you: "Line 42 was executed during tests." Test Shield tells you: "Line 42 changed. These 3 callers depend on it. They have zero tests. You didn't know about 2 of them." One is about what ran . The other is about what will break . I learned this the hard way during building: Python's dynamic nature means some callers are invisible to static analysis. getattr , importlib , decorator injection, monkey-patching — AST tracing can't see through those. So Test Shield doesn't pretend. Every run ends with a "honesty report": Tracing method: AST static analysis Dynamic call risks: 0 detected Known blind spots: getattr, importlib, decorators If it can't trace something, it tells you. No false confidence. Standalone — no Claude Code required git clone https://github.com/dominicharmon-commits/test-shield.git cd your-python-project python ../test-shield/scripts/analyze.py . With Claude Code /test-shield Zero dependencies. Pure Python stdlib. Python 3.10+. PRs welcome. MIT licensed. Built with Claude Code. Tested on a real production codebase. Stars appreciated. ⭐