Refactor timers into a simple tested object.

tests/utils/timer.test.ts

@@ -0,0 +1,67 @@
+import { afterAll, beforeAll, describe, expect, it, vi } from 'vitest';
+import { Timer } from '../../src/utils/timer';
+
+// @vitest-environment jsdom
+describe('Timer', () => {
+  beforeAll(() => {
+    vi.useFakeTimers();
+  });
+
+  afterAll(() => {
+    vi.useRealTimers();
+  });
+
+  it('should not be running on construct', () => {
+    const timer = new Timer();
+    expect(timer.isRunning()).toBeFalsy();
+  });
+
+  it('should fire when started', () => {
+    const timer = new Timer();
+    const handler = vi.fn();
+    timer.start(10, handler);
+
+    expect(timer.isRunning()).toBeTruthy();
+    expect(handler).not.toBeCalled();
+
+    vi.runOnlyPendingTimers();
+
+    expect(timer.isRunning()).toBeFalsy();
+    expect(handler).toBeCalled();
+  });
+
+  it('should fire repeatedly when started', () => {
+    const timer = new Timer();
+    const handler = vi.fn();
+    timer.startRepeated(10, handler);
+
+    expect(timer.isRunning()).toBeTruthy();
+    expect(handler).not.toBeCalled();
+
+    vi.runOnlyPendingTimers();
+
+    expect(timer.isRunning()).toBeTruthy();
+    expect(handler).toBeCalledTimes(1);
+
+    vi.runOnlyPendingTimers();
+
+    expect(timer.isRunning()).toBeTruthy();
+    expect(handler).toBeCalledTimes(2);
+  });
+
+  it('should not fire when stopped', () => {
+    const timer = new Timer();
+    const handler = vi.fn();
+    timer.start(10, handler);
+
+    expect(timer.isRunning()).toBeTruthy();
+    expect(handler).not.toBeCalled();
+
+    timer.stop();
+
+    vi.runOnlyPendingTimers();
+
+    expect(timer.isRunning()).toBeFalsy();
+    expect(handler).not.toBeCalled();
+  });
+});