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

> Source: <https://dev.to/dominic_harmon_18363706c7/i-built-a-claude-code-skill-that-finds-broken-callers-before-you-deploy-52a2>
> Published: 2026-06-27 02:33:31+00:00

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.* ⭐