[Tests] ChainingSearchTest - Improve stability (#3762)

* Improvement in test to make it more stable

* Decrease batch size

test/Microsoft.Health.Fhir.Shared.Tests.E2E/Rest/Search/ChainingSearchTests.cs

@@ -268,17 +268,52 @@ namespace Microsoft.Health.Fhir.Tests.E2E.Rest.Search
         [Fact]
         public async Task GivenANonSelectiveChainingQueryInCosmosDb_WhenSearched_ThenAnErrorShouldBeThrown()
         {
-            string query = $"subject:Patient.gender=male";
+            string tag = Guid.NewGuid().ToString();
+            string query = $"_tag={tag}&subject:Patient.gender=male";
 
             Patient resource = Samples.GetJsonSample("Patient-f001").ToPoco<Patient>();
-
-            // Create 1001 patients that exceed the sub-query limit
-            foreach (IEnumerable<int> batch in Enumerable.Range(1, 1001).TakeBatch(100))
+            resource.Meta = new Meta()
             {
-                await Task.WhenAll(batch.Select(_ => Client.CreateAsync(resource)));
+                Tag = new List<Coding>()
+                {
+                    new Coding("testTag", tag),
+                },
+            };
+
+            try
+            {
+                // Safe number to create resources without hitting any Cosmos DB limit, as the number of RUs assigned is low.
+                const int batchSize = 10;
+
+                // Create 1001 patients that exceed the sub-query limit
+                foreach (IEnumerable<int> batch in Enumerable.Range(1, 1001).TakeBatch(batchSize))
+                {
+                    await Task.WhenAll(batch.Select(_ => Client.CreateAsync(resource)));
+                }
+            }
+            catch (Exception ex)
+            {
+                throw new Exception($"Failed while creating resources: {ex.Message}", ex);
             }
 
-            await Assert.ThrowsAsync<FhirClientException>(async () => await Client.SearchAsync(ResourceType.Observation, query));
+            try
+            {
+                await Client.SearchAsync(ResourceType.Observation, query);
+
+                Assert.Fail("Test was expected to fail with a FhirException.");
+            }
+            catch (FhirClientException fce)
+            {
+                const string expectedMessage = "Sub-queries in a chained expression cannot return more than 1000 results";
+
+                Assert.True(
+                    fce.Message.Contains(expectedMessage),
+                    $"FhirClientException received is different than the one expected: Message: {fce.Message}");
+            }
+            catch (Exception ex)
+            {
+                Assert.Fail($"Unexpected exception thrown: {ex}");
+            }
         }
 
         [HttpIntegrationFixtureArgumentSets(DataStore.SqlServer, Format.Json)]