[chore] Add test to detect duplicate rule id (#2141)

* Add test to detect duplicate rule id

* Simplify duplicate testing

Author: Jym77

_rules/__tests__/unique-ids.js

@@ -0,0 +1,12 @@
+const getMarkdownData = require('../../utils/get-markdown-data')
+const rulesData = getMarkdownData(`./_rules`)
+
+describe('Rule ids verification', () => {
+	const duplicates = rulesData.filter(
+		(ruleData, idx) => rulesData.findIndex(r => r.frontmatter.id === ruleData.frontmatter.id) !== idx
+	)
+
+	test('Rule ids are unique', () => {
+		expect(duplicates.length, `Duplicated rules: ${duplicates.map(ruleData => ruleData.filename).join(', ')}`).toBe(0)
+	})
+})