build: add jest, tests

tests/randomInRange.test.ts

@@ -0,0 +1,7 @@
+import { expect, test } from "@jest/globals";
+import { randomInRange } from "../src";
+
+test("generates a random number in range", () => {
+  const randomNumber = randomInRange(1, 100);
+  expect(randomNumber >= 1 && randomNumber <= 100).toBeTruthy();
+});