added some tests to utils folder

src/core/utils/randId.test.ts

@@ -0,0 +1,44 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { randId } from "./randId";
+
+describe("randId", () => {
+  beforeEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it("returns a number", () => {
+    const result = randId();
+    expect(typeof result).toBe("number");
+  });
+
+  it("returns an integer", () => {
+    const result = randId();
+    expect(Number.isInteger(result)).toBe(true);
+  });
+
+  it("uses Math.random to generate the number", () => {
+    const mockRandom = vi.spyOn(Math, "random").mockReturnValue(0.5);
+    const result = randId();
+
+    expect(mockRandom).toHaveBeenCalled();
+    expect(result).toBe(Math.floor(0.5 * 1e9));
+  });
+
+  it("returns a value between 0 and 1e9 (exclusive)", () => {
+    const result = randId();
+    expect(result).toBeGreaterThanOrEqual(0);
+    expect(result).toBeLessThan(1e9);
+  });
+
+  it("returns different values on subsequent calls", () => {
+    vi.spyOn(Math, "random").mockRestore();
+
+    const results = new Set();
+
+    for (let i = 0; i < 100; i++) {
+      results.add(randId());
+    }
+
+    expect(results.size).toBeGreaterThan(95);
+  });
+});