retain defining no-undef in ESLint < 9

Author: mdjermanovic

tests/helpers/ruleTester.js

@@ -78,6 +78,11 @@ if (semver.major(eslintPkg.version) >= 9) {
           }
 
           const ruleIdSplit = ruleId.split('/');
+
+          if (ruleIdSplit.length !== 2) {
+            throw new Error('ruleId should be in the format: plugin-name/rule-name');
+          }
+
           const pluginName = ruleIdSplit[0];
           const ruleName = ruleIdSplit[1];
 

tests/lib/rules/jsx-no-undef.js

@@ -9,7 +9,11 @@
 // Requirements
 // -----------------------------------------------------------------------------
 
+const semver = require('semver');
+const eslintPkg = require('eslint/package.json');
 const RuleTester = require('../../helpers/ruleTester');
+const getRuleDefiner = require('../../helpers/getRuleDefiner');
+const getESLintCoreRule = require('../../helpers/getESLintCoreRule');
 const rule = require('../../../lib/rules/jsx-no-undef');
 
 const parsers = require('../../helpers/parsers');
@@ -28,6 +32,12 @@ const parserOptions = {
 
 const ruleTester = new RuleTester({ parserOptions });
 
+// In ESLint >= 9, it isn't possible to redefine a core rule, but it isn't necessary anyway since the core rules are certainly already available in the RuleTester/Linter
+if (semver.major(eslintPkg.version) < 9) {
+  const ruleDefiner = getRuleDefiner(ruleTester);
+  ruleDefiner.defineRule('no-undef', getESLintCoreRule('no-undef'));
+}
+
 ruleTester.run('jsx-no-undef', rule, {
   valid: parsers.all([
     {