feat(rule-tester): port checkDuplicateTestCases from ESLint

packages/eslint-plugin/tests/dedupeTestCases.ts

@@ -0,0 +1,14 @@
+export const dedupeTestCases = <T>(...caseArrays: (readonly T[])[]): T[] => {
+ const cases = caseArrays.flat();
+ const dedupedCases = Object.values(
+ Object.fromEntries(
+ cases.map(testCase => [JSON.stringify(testCase), testCase]),
+ ),
+ );
+ if (cases.length === dedupedCases.length) {
+ throw new Error(
+ '`dedupeTestCases` is not necessary — no duplicate test cases detected!',
+ );
+ }
+ return dedupedCases;
+};