✅ Add vitest and initial tests

src/tools/shared/time/stopwatch.tool.test.ts

@@ -0,0 +1,26 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { Stopwatch } from './stopwatch.tool';
+
+describe('stopwatch', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it.concurrent('should be elapsed time between start and current', () => {
+    // arrange
+    vi.setSystemTime(new Date(2023, 2, 26, 0, 0, 0));
+    const stopwatch = new Stopwatch();
+
+    // act
+    vi.setSystemTime(new Date(2023, 2, 26, 0, 0, 2));
+    const milliseconds = stopwatch.getEllapsedMilliseconds();
+
+    // assert
+    expect(milliseconds).toBe(2000);
+  });
+});