# ChangeGuard report — Sample: A pricing refactor that quietly breaks its callers
> **Review priority: HIGH** — 2 high-severity deterministic or heuristic finding(s).
> Severity and confidence are categorical rule judgements, not probabilities of failure.
| | |
|---|---|
| Files changed | 3 (+24 −5) — Python |
| Mode | Full context (repository snapshot) |
| Findings | 13 — deterministic 9 · heuristic 4 · AI 0 |
| Changed symbols | 5 (1 with breaking signature changes) |
| Patch coverage | 21.1% (4/19 changed executable lines, from uploaded report) |
| AI synthesis | completed — ollama / llama3.2:3b; 2/2 claims passed grounding checks |
| Engine | ChangeGuard 0.1.0 · ruleset 2026.10.4 · report schema 1.0 |
## Findings
### 1. [HIGH] 2 call site(s) incompatible with new signature of `format_price`
`CG-API-001` · deterministic · confidence high · `src/billing/pricing.py:16`
`format_price` changed (parameter `currency` removed; required parameter `locale` added). 2 of 3 call site(s) in the repository no longer match the new signature.
**Why it matters.** A caller still uses the old calling convention. In Python this raises TypeError at call time; in TypeScript it fails compilation.
**Failure scenario.** src/billing/invoice.py:9 still calls `format_price` the old way: it passes unexpected keyword argument `currency`. Python raises TypeError when that line runs.
**Evidence**
- **E2** Signature of format_price changed — `src/billing/pricing.py:16` _(source: tree-sitter structural diff)_
```python
def format_price(amount: Decimal, locale: str) -> str:
"""Render an amount using the symbol for the caller's locale."""
```
- **E3** Call site src/billing/invoice.py:9 in render_line — `src/billing/invoice.py:9` _(source: repository snapshot (tree-sitter))_
```python
def render_line(description: str, amount: Decimal, currency: str) -> str:
return f"{description}: {format_price(amount, currency=currency)}"
```
- **E4** Call site tests/test_pricing.py:18 in test_format_price_defaults_to_usd — `tests/test_pricing.py:18` _(source: repository snapshot (tree-sitter))_
```python
def test_format_price_defaults_to_usd():
assert format_price(Decimal("5")) == "$5.00"
assert format_price(Decimal("5"), "EUR") == "€5.00"
```
**Suggested regression check.** Update the incompatible callers, then add a regression test that calls `format_price` the way those callers do.
```python
from billing.pricing import format_price
def test_format_price_matches_callers():
# mirror the argument shape used at the call sites listed in the evidence
result = format_price(amount=..., locale=...)
assert result == ... # expected value for these inputs
```
AI analysis (llama3.2:3b, passed grounding checks, confidence high)
The new signature of `format_price` changes the required parameter from `currency` to `locale`, making it incompatible with existing call sites.
_Failure scenario:_ A function calls `format_price` with a `currency` argument, but the function is expecting a `locale` argument. This will cause a TypeError when trying to execute the function.
_Uncertainty:_ low