[SavedObjects] Create serverless roots for jest integration tests (#164157)

## Summary

Introduce basic utils for instantiating serverless servers ;). Also adds
a simple smoke test (that is currently skipped) demonstrating usage.

## How to test

Check this branch out locally, un`skip` the smoke test and run:

```
yarn test:jest_integration ./src/core/server/integration_tests/saved_objects/serverless/migrations
```

Note: the test cannot be unskipped as we are blocking on
https://github.com/elastic/kibana/pull/162673 but we would like to
prepare our tests so long --- they can be locally executed.

## Follow up

* Create Jest integration tests using these helpers for all migration
actions (see
`packages/core/saved-objects/core-saved-objects-migration-server-internal/src/zdt/actions`
and
`packages/core/saved-objects/core-saved-objects-migration-server-internal/src/actions`).
* Migrate our existing ZDT tests to run against serverless Elasticsearch

## Related

https://github.com/elastic/kibana/pull/162673

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

packages/core/test-helpers/core-test-helpers-kbn-server/index.ts

@@ -12,7 +12,15 @@ export {
   createRoot,
   createRootWithCorePlugins,
   createTestServers,
+  createTestServerlessInstances,
   request,
 } from './src';
 
-export type { HttpMethod, TestElasticsearchUtils, TestKibanaUtils, TestUtils } from './src';
+export type {
+  HttpMethod,
+  TestElasticsearchUtils,
+  TestKibanaUtils,
+  TestUtils,
+  TestServerlessESUtils,
+  TestServerlessKibanaUtils,
+} from './src';

packages/core/test-helpers/core-test-helpers-kbn-server/src/create_serverless_root.ts

@@ -0,0 +1,100 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+import { defaultsDeep } from 'lodash';
+import { Cluster } from '@kbn/es';
+import Path from 'path';
+import { REPO_ROOT } from '@kbn/repo-info';
+import { ToolingLog } from '@kbn/tooling-log';
+import execa from 'execa';
+import { CliArgs } from '@kbn/config';
+import { createRoot, type TestElasticsearchUtils, type TestKibanaUtils } from './create_root';
+
+export type TestServerlessESUtils = Pick<TestElasticsearchUtils, 'stop' | 'es'>;
+export type TestServerlessKibanaUtils = TestKibanaUtils;
+export interface TestServerlessUtils {
+  startES: () => Promise<TestServerlessESUtils>;
+  startKibana: (abortSignal?: AbortSignal) => Promise<TestServerlessKibanaUtils>;
+}
+
+/**
+ * See docs in {@link TestUtils}. This function provides the same utilities but
+ * configured for serverless.
+ *
+ * @note requires a Docker installation to be running
+ */
+export function createTestServerlessInstances({
+  adjustTimeout,
+}: {
+  adjustTimeout: (timeout: number) => void;
+}): TestServerlessUtils {
+  const esUtils = createServerlessES();
+  const kbUtils = createServerlessKibana();
+  adjustTimeout?.(120_000);
+  return {
+    startES: async () => {
+      const { stop } = await esUtils.start();
+      return {
+        es: esUtils.es,
+        stop,
+      };
+    },
+    startKibana: async (abortSignal) => {
+      abortSignal?.addEventListener('abort', async () => await kbUtils.shutdown());
+      await kbUtils.preboot();
+      const coreSetup = await kbUtils.setup();
+      const coreStart = await kbUtils.start();
+      return {
+        root: kbUtils,
+        coreSetup,
+        coreStart,
+        stop: kbUtils.shutdown.bind(kbUtils),
+      };
+    },
+  };
+}
+
+function createServerlessES() {
+  const log = new ToolingLog({
+    level: 'info',
+    writeTo: process.stdout,
+  });
+  const es = new Cluster({ log });
+  return {
+    es,
+    start: async () => {
+      await es.runServerless({
+        basePath: Path.join(REPO_ROOT, '.es/es_test_serverless'),
+      });
+      return {
+        stop: async () => {
+          // hack to stop the ES cluster
+          await execa('docker', ['container', 'stop', 'es01', 'es02', 'es03']);
+        },
+      };
+    },
+  };
+}
+
+const defaults = {
+  server: {
+    restrictInternalApis: true,
+    versioned: {
+      versionResolution: 'newest',
+      strictClientVersionCheck: false,
+    },
+  },
+  migrations: {
+    algorithm: 'zdt',
+  },
+  elasticsearch: {
+    serviceAccountToken: 'BEEF',
+  },
+};
+function createServerlessKibana(settings = {}, cliArgs: Partial<CliArgs> = {}) {
+  return createRoot(defaultsDeep(settings, defaults), { ...cliArgs, serverless: true });
+}

packages/core/test-helpers/core-test-helpers-kbn-server/src/index.ts

@@ -15,4 +15,12 @@ export {
   request,
 } from './create_root';
 
+export { createTestServerlessInstances } from './create_serverless_root';
+
+export type {
+  TestServerlessUtils,
+  TestServerlessESUtils,
+  TestServerlessKibanaUtils,
+} from './create_serverless_root';
+
 export type { HttpMethod, TestElasticsearchUtils, TestKibanaUtils, TestUtils } from './create_root';

packages/core/test-helpers/core-test-helpers-kbn-server/tsconfig.json

@@ -18,6 +18,7 @@
     "@kbn/core-root-server-internal",
     "@kbn/repo-info",
     "@kbn/repo-packages",
+    "@kbn/es",
   ],
   "exclude": [
     "target/**/*",

src/core/server/integration_tests/saved_objects/serverless/migrations/jest.integration.config.js

@@ -0,0 +1,19 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+module.exports = {
+  // TODO replace the line below with
+  // preset: '@kbn/test/jest_integration_node
+  // to do so, we must fix all integration tests first
+  // see https://github.com/elastic/kibana/pull/130255/
+  preset: '@kbn/test/jest_integration',
+  rootDir: '../../../../../../..',
+  roots: ['<rootDir>/src/core/server/integration_tests/saved_objects/serverless/migrations'],
+  // must override to match all test given there is no `integration_tests` subfolder
+  testMatch: ['**/*.test.{js,mjs,ts,tsx}'],
+};

src/core/server/integration_tests/saved_objects/serverless/migrations/smoke.test.ts

@@ -0,0 +1,39 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import {
+  request,
+  TestServerlessESUtils,
+  TestServerlessKibanaUtils,
+  createTestServerlessInstances,
+} from '@kbn/core-test-helpers-kbn-server';
+
+/**
+ * Until we merge https://github.com/elastic/kibana/pull/162673 this test should remain skipped.
+ */
+describe.skip('smoke', () => {
+  let serverlessES: TestServerlessESUtils;
+  let serverlessKibana: TestServerlessKibanaUtils;
+  let root: TestServerlessKibanaUtils['root'];
+  beforeEach(async () => {
+    const { startES, startKibana } = createTestServerlessInstances({
+      adjustTimeout: jest.setTimeout,
+    });
+    serverlessES = await startES();
+    serverlessKibana = await startKibana();
+    root = serverlessKibana.root;
+  });
+  afterEach(async () => {
+    await serverlessES?.stop();
+    await serverlessKibana?.stop();
+  });
+  test('it can start Kibana and ES serverless', async () => {
+    const { body } = await request.get(root, '/api/status').expect(200);
+    expect(body).toMatchObject({ status: { overall: { level: 'available' } } });
+  });
+});