Add Upgrade Assistant API integration test to ensure the reindex oper…

…ation saved object can handle immense error messages (elastic#72347)

x-pack/test/api_integration/apis/index.js

@@ -32,5 +32,6 @@ export default function ({ loadTestFile }) {
     loadTestFile(require.resolve('./endpoint'));
     loadTestFile(require.resolve('./ingest_manager'));
     loadTestFile(require.resolve('./lists'));
+    loadTestFile(require.resolve('./upgrade_assistant'));
   });
 }

x-pack/test/api_integration/apis/upgrade_assistant/index.ts

@@ -0,0 +1,13 @@
+/*
+ * 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 { FtrProviderContext } from '../../ftr_provider_context';
+
+export default function ({ loadTestFile }: FtrProviderContext) {
+  describe('Upgrade Assistant', () => {
+    loadTestFile(require.resolve('./upgrade_assistant'));
+  });
+}

x-pack/test/api_integration/apis/upgrade_assistant/upgrade_assistant.ts

@@ -0,0 +1,34 @@
+/*
+ * 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 expect from '@kbn/expect';
+
+import { FtrProviderContext } from '../../ftr_provider_context';
+import { reindexOperationWithLargeErrorMessage } from './reindex_operation_with_large_error_message';
+
+export default function ({ getService }: FtrProviderContext) {
+  const es = getService('legacyEs');
+
+  describe('Reindex operation saved object', function () {
+    const dotKibanaIndex = '.kibana';
+    const fakeSavedObjectId = 'fakeSavedObjectId';
+
+    after(async () => {
+      // Clean up the fake saved object we created. This will error if the test failed.
+      return await es.delete({ index: dotKibanaIndex, id: fakeSavedObjectId });
+    });
+
+    it('is indexed successfully with immense error message', async () => {
+      // Guards against regression of https://github.com/elastic/kibana/pull/71710.
+      const result = await es.create({
+        index: dotKibanaIndex, // In normal operation this would be the .kibana-n index.
+        id: fakeSavedObjectId,
+        body: reindexOperationWithLargeErrorMessage,
+      });
+      expect(result).to.be.ok();
+    });
+  });
+}