[SLO] Fix get_slo.ts api integration test (#178059)

## Summary

This PR introduces a `waitForIndexToBeEmpty` function to allow for the
SLO to be completely deleted before letting the test move on.

Fixes #176763

x-pack/test/api_integration/apis/slos/get_slo.ts

@@ -14,8 +14,7 @@ import { SloEsClient } from './helper/es';
 import { sloData } from './fixtures/create_slo';
 
 export default function ({ getService }: FtrProviderContext) {
-  // FLAKY: https://github.com/elastic/kibana/issues/177806
-  describe.skip('Get SLOs', function () {
+  describe('Get SLOs', function () {
     this.tags('skipCloud');
 
     const supertestAPI = getService('supertest');

x-pack/test/api_integration/apis/slos/helper/wait_for_index_state.ts

@@ -0,0 +1,53 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import type { Client } from '@elastic/elasticsearch';
+import type {
+  AggregationsAggregate,
+  SearchResponse,
+} from '@elastic/elasticsearch/lib/api/typesWithBodyKey';
+import pRetry from 'p-retry';
+
+export async function waitForDocumentInIndex<T>({
+  esClient,
+  indexName,
+  docCountTarget = 1,
+}: {
+  esClient: Client;
+  indexName: string;
+  docCountTarget?: number;
+}): Promise<SearchResponse<T, Record<string, AggregationsAggregate>>> {
+  return pRetry(
+    async () => {
+      const response = await esClient.search<T>({ index: indexName, rest_total_hits_as_int: true });
+      if (!response.hits.total || response.hits.total < docCountTarget) {
+        throw new Error('No hits found');
+      }
+      return response;
+    },
+    { retries: 10 }
+  );
+}
+
+export async function waitForIndexToBeEmpty<T>({
+  esClient,
+  indexName,
+}: {
+  esClient: Client;
+  indexName: string;
+}): Promise<SearchResponse<T, Record<string, AggregationsAggregate>>> {
+  return pRetry(
+    async () => {
+      const response = await esClient.search<T>({ index: indexName, rest_total_hits_as_int: true });
+      if (response.hits.total != null && response.hits.total > 0) {
+        throw new Error(`Found ${response.hits.total} docs.`);
+      }
+      return response;
+    },
+    { retries: 10 }
+  );
+}

x-pack/test/api_integration/services/slo.ts

@@ -6,10 +6,13 @@
  */
 
 import { CreateSLOInput, FindSLODefinitionsResponse } from '@kbn/slo-schema';
+import { SLO_SUMMARY_DESTINATION_INDEX_NAME } from '@kbn/observability-plugin/common/slo/constants';
+import { waitForIndexToBeEmpty } from '../apis/slos/helper/wait_for_index_state';
 import { FtrProviderContext } from '../ftr_provider_context';
 
 export function SloApiProvider({ getService }: FtrProviderContext) {
   const supertest = getService('supertest');
+  const esClient = getService('es');
 
   return {
     async create(params: CreateSLOInput) {
@@ -44,6 +47,7 @@ export function SloApiProvider({ getService }: FtrProviderContext) {
           .send()
           .expect(204);
       }
+      await waitForIndexToBeEmpty({ esClient, indexName: SLO_SUMMARY_DESTINATION_INDEX_NAME });
     },
   };
 }