feat: Add App class to start and stop the server

test/unit/init/App.test.ts

@@ -0,0 +1,25 @@
+import { App } from '../../../src/init/App';
+import type { Finalizable } from '../../../src/init/final/Finalizable';
+import type { Initializer } from '../../../src/init/Initializer';
+
+describe('An App', (): void => {
+  let initializer: Initializer;
+  let finalizer: Finalizable;
+  let app: App;
+
+  beforeEach(async(): Promise<void> => {
+    initializer = { handleSafe: jest.fn() } as any;
+    finalizer = { finalize: jest.fn() };
+    app = new App(initializer, finalizer);
+  });
+
+  it('can start with the initializer.', async(): Promise<void> => {
+    await expect(app.start()).resolves.toBeUndefined();
+    expect(initializer.handleSafe).toHaveBeenCalledTimes(1);
+  });
+
+  it('can stop with the finalizer.', async(): Promise<void> => {
+    await expect(app.stop()).resolves.toBeUndefined();
+    expect(finalizer.finalize).toHaveBeenCalledTimes(1);
+  });
+});