diff --git a/tests/index.test.js b/tests/index.test.js
new file mode 100644
index 0000000..652f8de
--- /dev/null
+++ b/tests/index.test.js
@@ -0,0 +1,62 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { parseConfig, shutdown } from "../src/index.js";
+
+describe("parseConfig", () => {
+  const originalEnv = { ...process.env };
+
+  afterEach(() => {
+    process.env = { ...originalEnv };
+  });
+
+  it("returns defaults when env vars are absent", () => {
+    delete process.env.PORT;
+    delete process.env.WS_HEARTBEAT_MS;
+    delete process.env.MAX_PAYLOAD_BYTES;
+    const config = parseConfig();
+    expect(config).toEqual({ port: 8080, heartbeatMs: 30000, maxPayloadBytes: 1024 });
+  });
+
+  it("reads values from environment variables", () => {
+    process.env.PORT = "9090";
+    process.env.WS_HEARTBEAT_MS = "15000";
+    process.env.MAX_PAYLOAD_BYTES = "2048";
+    const config = parseConfig();
+    expect(config).toEqual({ port: 9090, heartbeatMs: 15000, maxPayloadBytes: 2048 });
+  });
+
+  it("returns integer values", () => {
+    const { port, heartbeatMs, maxPayloadBytes } = parseConfig();
+    expect(Number.isInteger(port)).toBe(true);
+    expect(Number.isInteger(heartbeatMs)).toBe(true);
+    expect(Number.isInteger(maxPayloadBytes)).toBe(true);
+  });
+});
+
+describe("shutdown", () => {
+  let mockWss;
+  let exitSpy;
+
+  beforeEach(() => {
+    mockWss = { close: vi.fn((cb) => cb()) };
+    exitSpy = vi.spyOn(process, "exit").mockImplementation(() => {});
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.useRealTimers();
+  });
+
+  it("calls wss.close and then process.exit(0)", () => {
+    shutdown(mockWss, "SIGTERM");
+    expect(mockWss.close).toHaveBeenCalledOnce();
+    expect(exitSpy).toHaveBeenCalledWith(0);
+  });
+
+  it("forces process.exit(1) after 5 seconds if server does not close", () => {
+    mockWss.close = vi.fn(); // does NOT call callback
+    shutdown(mockWss, "SIGINT");
+    vi.advanceTimersByTime(5000);
+    expect(exitSpy).toHaveBeenCalledWith(1);
+  });
+});