Add jsdoc and unit tests for util functions

utils/random.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from 'bun:test';
+import { randomInt } from './random.ts';
+
+describe('random utils', () => {
+  it('randomInt', () => {
+    const from = -2;
+    const to = 6;
+    for (let i = 0; i < 20; i++) {
+      const number = randomInt(from, to);
+      expect(number).toBeNumber();
+      expect(number).toBeFinite();
+      expect(number).toBeInteger();
+      expect(number).toBeGreaterThanOrEqual(from);
+      expect(number).toBeLessThan(to);
+    }
+  });
+});