feat: Add App class to start and stop the server

test/unit/init/final/ParallelFinalizer.test.ts

@@ -0,0 +1,30 @@
+import type { Finalizable } from '../../../../src/init/final/Finalizable';
+import { ParallelFinalizer } from '../../../../src/init/final/ParallelFinalizer';
+
+describe('A ParallelFinalizer', (): void => {
+  let finalizers: Finalizable[];
+  let finalizer: ParallelFinalizer;
+  let results: number[];
+
+  beforeEach(async(): Promise<void> => {
+    results = [];
+    finalizers = [
+      { finalize: jest.fn((): any => results.push(0)) },
+      { finalize: jest.fn((): any => results.push(1)) },
+    ];
+
+    finalizer = new ParallelFinalizer(finalizers);
+  });
+
+  it('is finished when all finalizers are finished.', async(): Promise<void> => {
+    await expect(finalizer.finalize()).resolves.toBeUndefined();
+    expect(finalizers[0].finalize).toHaveBeenCalledTimes(1);
+    expect(finalizers[1].finalize).toHaveBeenCalledTimes(1);
+    expect(results).toEqual([ 0, 1 ]);
+  });
+
+  it('works if there are no input finalizers.', async(): Promise<void> => {
+    finalizer = new ParallelFinalizer();
+    await expect(finalizer.finalize()).resolves.toBeUndefined();
+  });
+});