feat: add CompositeAsyncHandler to support multiple handlers

test/unit/util/AsyncHandler.test.ts

@@ -0,0 +1,30 @@
+import { AsyncHandler } from '../../../src/util/AsyncHandler';
+import { StaticAsyncHandler } from '../../util/StaticAsyncHandler';
+
+describe('An AsyncHandler', (): void => {
+  it('calls canHandle and handle when handleSafe is called.', async (): Promise<void> => {
+    const handlerTrue: AsyncHandler<any, any> = new StaticAsyncHandler(true, null);
+    const canHandleFn = jest.fn(async (input: any): Promise<void> => input);
+    const handleFn = jest.fn(async (input: any): Promise<any> => input);
+
+    handlerTrue.canHandle = canHandleFn;
+    handlerTrue.handle = handleFn;
+    await expect(handlerTrue.handleSafe('test')).resolves.toBe('test');
+    expect(canHandleFn).toHaveBeenCalledTimes(1);
+    expect(handleFn).toHaveBeenCalledTimes(1);
+  });
+
+  it('does not call handle when canHandle errors during a handleSafe call.', async (): Promise<void> => {
+    const handlerFalse: AsyncHandler<any, any> = new StaticAsyncHandler(false, null);
+    const canHandleFn = jest.fn(async (): Promise<void> => {
+      throw new Error('test');
+    });
+    const handleFn = jest.fn(async (input: any): Promise<any> => input);
+
+    handlerFalse.canHandle = canHandleFn;
+    handlerFalse.handle = handleFn;
+    await expect(handlerFalse.handleSafe('test')).rejects.toThrow(Error);
+    expect(canHandleFn).toHaveBeenCalledTimes(1);
+    expect(handleFn).toHaveBeenCalledTimes(0);
+  });
+});