docs: no pass-through tests — every test must assert meaningful behaviour

Author: ChrisHeral

CLAUDE.md

@@ -102,6 +102,7 @@ When generating or modifying code in this project:
 - Repository → run the contract suite against every new implementation
 - New non-trivial validation rule → add a Hypothesis test (`@given`) to explore edge cases
 - Never use `unittest.mock` on domain code — if it's hard to test, it's a design signal
+- Every test must assert a meaningful behaviour — no pass-through tests written solely for coverage
 - New hot path (loop, algorithm, aggregation) → add a benchmark in `tests/examples/test_benchmarks.py`
 
 **Security**

QUALITY.md

@@ -65,6 +65,15 @@
 | pytest-benchmark | manual (`make benchmark`) | no | tests/examples/test_benchmarks.py |
 | E2E tests | CI (main) | no | tests/e2e/ |
 
+## Test philosophy
+
+Coverage is a proxy, not a goal. A test has value only if it can fail for the right reason.
+
+- **Assert behaviour, not implementation** — test what the code does, not how it does it
+- **No pass-through tests** — a test that always passes regardless of the code is worse than no test
+- **One clear intent per test** — if a test breaks, it must be obvious why
+- **Coverage ≥ 80% is a floor, not a target** — chasing 100% produces noise; mutmut reveals gaps that coverage misses
+
 ## Local commands
 
 ```bash