test: add test for validLink

jest.config.js

@@ -0,0 +1,5 @@
+/** @type {import('ts-jest').JestConfigWithTsJest} */
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+};

test/validLink.test.ts

@@ -0,0 +1,6 @@
+import {describe, expect, test} from '@jest/globals';
+import validLink from "../lib/url/valid_link";
+
+test("Plain, full URL", () => {
+    expect(validLink("https://example.com/about-us")).toBe(true);
+});