[Ingest Manager] prevent crash on unhandled rejection from setupInges…

…tManager (#74300) (#74350)

* Add test to ensure setup rejects if errors thrown.

* Return the promise from setup so test passes

x-pack/plugins/ingest_manager/server/services/setup.test.ts

@@ -0,0 +1,44 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+import { setupIngestManager } from './setup';
+import { savedObjectsClientMock } from 'src/core/server/mocks';
+
+describe('setupIngestManager', () => {
+  it('returned promise should reject if errors thrown', async () => {
+    const { savedObjectsClient, callClusterMock } = makeErrorMocks();
+    const setupPromise = setupIngestManager(savedObjectsClient, callClusterMock);
+    await expect(setupPromise).rejects.toThrow('mocked');
+  });
+});
+
+function makeErrorMocks() {
+  jest.mock('./app_context'); // else fails w/"Logger not set."
+  jest.mock('./epm/registry/registry_url', () => {
+    return {
+      fetchUrl: () => {
+        throw new Error('mocked registry#fetchUrl');
+      },
+    };
+  });
+
+  const callClusterMock = jest.fn();
+  const savedObjectsClient = savedObjectsClientMock.create();
+  savedObjectsClient.find = jest.fn().mockImplementation(() => {
+    throw new Error('mocked SO#find');
+  });
+  savedObjectsClient.get = jest.fn().mockImplementation(() => {
+    throw new Error('mocked SO#get');
+  });
+  savedObjectsClient.update = jest.fn().mockImplementation(() => {
+    throw new Error('mocked SO#update');
+  });
+
+  return {
+    savedObjectsClient,
+    callClusterMock,
+  };
+}

x-pack/plugins/ingest_manager/server/services/setup.ts

@@ -127,6 +127,11 @@ export async function setupIngestManager(
     // if anything errors, reject/fail
     onSetupReject(error);
   }
+
+  // be sure to return the promise because it has the resolved/rejected status attached to it
+  // otherwise, we effectively return success every time even if there are errors
+  // because `return undefined` -> `Promise.resolve(undefined)` in an `async` function
+  return setupIngestStatus;
 }
 
 export async function setupFleet(