R6.4: Hermetic test state isolation

Short answer: Isolate DB/state paths per test in setUp/addCleanup. Tests that share a database or a state folder pass or fail depending on their order.

Group: Testing and hermeticity. Status: stable. Generated from the rule definitions; do not edit by hand.

Playground: https://brevio.pro/tools/agent-guard-playground?rule=R6.4

What it catches

Hermetic test state isolation: isolate DB/state paths per test in setUp/addCleanup.

Why

Tests that share a database or a state folder pass or fail depending on their order.

A bad example

const path = '/tmp/state.json';

A good example

const path = join(mkdtempSync(join(tmpdir(), 't-')), 'state.json');

How it is checked

A one-line card in the prompt of a slice that touches matching files (dev_rules.slice_micro_rules).

How to silence it

A person can silence one finding with brevio-core: ignore R6.4 -- reason on the line or the line above. Without the reason it does not count. An agent cannot silence it: the agent hook and the MCP tools never honour the comment, and a pull request that adds one is reported until a reviewer allows it. Fixing the code is still the better answer.

To change what the rule flags, edit its definition in dev_rules.py or code_rules/__init__.py. That is a code change and is reviewed like one.

R6.5 Post-incident regression crystallization
R6.1 Real production import gate
R6.2 Mutation side-effect assertions
R6.3 Deterministic condition waits
Every rule