The **eslint-config-rule-tester** (ConfigTester) is a utility that lets developers unit‑test individual ESLint rules directly from a configuration object instead of writing separate rule modules. By supplying a rule name, a config object containing only that rule, and a set of valid/invalid code samples, it runs the rule against the samples and reports any mismatches—useful for teams that maintain complex shared ESLint configs (e.g., the Agoric “eslint‑config‑jessie” preset). It’s aimed at ESLint plugin/ configuration authors who want automated tests for their config‑based rule setups.