diff --git a/test/helpers.spec.ts b/test/helpers.spec.ts
index ce8fb73387e..15c26874d2f 100644
--- a/test/helpers.spec.ts
+++ b/test/helpers.spec.ts
@@ -2,6 +2,7 @@ import { afterEach, describe, expect, it } from 'vitest';
 import { faker, FakerError } from '../src';
 import { luhnCheck } from '../src/modules/helpers/luhn-check';
 import { seededTests } from './support/seededRuns';
+import './vitest-extensions';
 
 const NON_SEEDED_BASED_RUN = 5;
 
@@ -142,7 +143,7 @@ describe('helpers', () => {
           });
 
           // Check uniqueness
-          expect(subset).toHaveLength(new Set(subset).size);
+          expect(subset).not.toContainDuplicates();
         });
 
         it('should return a subset of fixed length with random elements in the array', () => {
@@ -345,8 +346,8 @@ describe('helpers', () => {
           const input = ['a', 'a', 'a', 'a,', 'a', 'a', 'a', 'a', 'b'];
           const length = 2;
           const unique = faker.helpers.uniqueArray(input, length);
+          expect(unique).not.toContainDuplicates();
           expect(unique).toHaveLength(length);
-          expect(new Set(unique).size).toBe(length);
         });
 
         it('definition array returns unique array', () => {
@@ -355,31 +356,30 @@ describe('helpers', () => {
             faker.definitions.hacker.noun,
             length
           );
+          expect(unique).not.toContainDuplicates();
           expect(unique).toHaveLength(length);
-          expect(new Set(unique).size).toBe(length);
         });
 
         it('function returns unique array', () => {
           const length = faker.datatype.number({ min: 1, max: 6 });
           const unique = faker.helpers.uniqueArray(faker.lorem.word, length);
+          expect(unique).not.toContainDuplicates();
           expect(unique).toHaveLength(length);
-          expect(new Set(unique).size).toBe(length);
         });
 
         it('empty array returns empty array', () => {
           const input = [];
           const length = faker.datatype.number({ min: 1, max: 6 });
           const unique = faker.helpers.uniqueArray(input, length);
-          expect(unique).toHaveLength(input.length);
-          expect(new Set(unique).size).toBe(input.length);
+          expect(unique).toHaveLength(0);
         });
 
         it('length longer than source returns max length', () => {
           const input = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j'];
           const length = input.length + 1;
           const unique = faker.helpers.uniqueArray(input, length);
+          expect(unique).not.toContainDuplicates();
           expect(unique).toHaveLength(input.length);
-          expect(new Set(unique).size).toBe(input.length);
         });
 
         it('works as expected when seeded', () => {
diff --git a/test/locales.spec.ts b/test/locales.spec.ts
index 17115809405..9e290c5a559 100644
--- a/test/locales.spec.ts
+++ b/test/locales.spec.ts
@@ -2,6 +2,7 @@ import { describe, expect, it } from 'vitest';
 import type { LocaleDefinition } from '../src';
 import { faker } from '../src';
 import allLocales from '../src/locales';
+import './vitest-extensions';
 
 // Remark: actual use of locales functionality is currently tested in all.functional.js test
 
@@ -32,16 +33,7 @@ describe('locale', () => {
             describe(definitionName, () => {
               function testArraySample<T>(arr: T[]) {
                 it('should not have duplicate entries', () => {
-                  const uniques = new Set(arr);
-                  const duplications = arr.filter(
-                    (entry) => !uniques.delete(entry)
-                  );
-                  const uniqueDuplication = [...new Set(duplications)];
-
-                  expect(
-                    uniqueDuplication,
-                    `Duplicated values are: [${uniqueDuplication.join(', ')}]`
-                  ).toEqual([]);
+                  expect(arr).not.toContainDuplicates();
                 });
               }
 
diff --git a/test/vitest-extensions.ts b/test/vitest-extensions.ts
new file mode 100644
index 00000000000..b33919efb00
--- /dev/null
+++ b/test/vitest-extensions.ts
@@ -0,0 +1,33 @@
+import { expect } from 'vitest';
+
+expect.extend({
+  toContainDuplicates<T>(received: T[]) {
+    const { isNot } = this;
+
+    const uniques = new Set(received);
+    const duplications = received.filter((entry) => !uniques.delete(entry));
+    const uniqueDuplication = [...new Set(duplications)];
+
+    return {
+      pass: uniqueDuplication.length !== 0,
+      message: () =>
+        isNot
+          ? `Duplicated values are [${uniqueDuplication.join(', ')}]`
+          : `No duplicate values in [${received.join(', ')}]`,
+    };
+  },
+});
+
+interface CustomMatchers {
+  toContainDuplicates(): void;
+}
+
+declare global {
+  // eslint-disable-next-line @typescript-eslint/no-namespace
+  namespace Vi {
+    // eslint-disable-next-line @typescript-eslint/no-empty-interface
+    interface Assertion extends CustomMatchers {}
+    // eslint-disable-next-line @typescript-eslint/no-empty-interface
+    interface AsymmetricMatchersContaining extends CustomMatchers {}
+  }
+}