test: reproduce opensearch-projectGH-281 TermQuery with Value of empt…

…y string serializes as <null>

tests/Tests.Reproduce/GitHubIssue281.cs

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+/* SPDX-License-Identifier: Apache-2.0
+*
+* The OpenSearch Contributors require contributions made to
+* this file be licensed under the Apache-2.0 license or a
+* compatible open source license.
+*/
+/*
+* Modifications Copyright OpenSearch Contributors. See
+* GitHub history for details.
+*
+*  Licensed to Elasticsearch B.V. under one or more contributor
+*  license agreements. See the NOTICE file distributed with
+*  this work for additional information regarding copyright
+*  ownership. Elasticsearch B.V. licenses this file to you under
+*  the Apache License, Version 2.0 (the "License"); you may
+*  not use this file except in compliance with the License.
+*  You may obtain a copy of the License at
+*
+* 	http://www.apache.org/licenses/LICENSE-2.0
+*
+*  Unless required by applicable law or agreed to in writing,
+*  software distributed under the License is distributed on an
+*  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+*  KIND, either express or implied.  See the License for the
+*  specific language governing permissions and limitations
+*  under the License.
+*/
+
+using System;
+using System.Linq;
+using System.Text;
+using System.Text.Json.Serialization;
+using OpenSearch.OpenSearch.Xunit.XunitPlumbing;
+using OpenSearch.Net;
+using FluentAssertions;
+using OpenSearch.Client;
+using Xunit;
+
+namespace Tests.Reproduce
+{
+	public class GithubIssue281
+	{
+		public class SampleDomainObject
+		{
+			[JsonPropertyName("first_name")]
+			public string FirstName { get; set; }
+
+			[JsonPropertyName("last_name")]
+			public string LastName { get; set; }
+		}
+
+		[U]
+		public void GithubIssu281_MustNotWithTermQueryAndEmptyValueShouldBeInRequestBody()
+		{
+			var connectionSettings = new ConnectionSettings(new InMemoryConnection()).DisableDirectStreaming();
+			var client = new OpenSearchClient(connectionSettings);
+
+			var action = () =>
+				client.Search<SampleDomainObject>(s => s
+					.Query(q => q
+						.Bool(b => b
+							.Must(m => m.Exists(e => e.Field("last_name")))
+							.MustNot(m => m.Term(t => t.Field("last_name.keyword").Value(string.Empty)))
+						)
+					)
+					.Index("index")
+					.Source(sfd => null)
+				);
+
+			var response = action.Should().NotThrow().Subject;
+
+			var json = Encoding.UTF8.GetString(response.ApiCall.RequestBodyInBytes);
+			json.Should()
+				.Be(
+					@"{""query"":{""bool"":{""must"":[{""exists"":{""field"":""last_name""}}],""must_not"":[{""term"":{""last_name.keyword"":{""value"":""""}}}]}}}");
+		}
+
+		[U]
+		public void GithubIssue281_MustNotTermQueryAndEmptyValueShouldBeRegisteredAsNonNull()
+		{
+			Func<SearchDescriptor<SampleDomainObject>, ISearchRequest> selector = s => s
+				.Query(q => q
+					.Bool(b => b
+						.Must(m => m.Exists(e => e.Field("last_name")))
+						.MustNot(m => m.Term(t => t.Field("last_name.keyword").Value(string.Empty)))
+					)
+				)
+				.Index("index")
+				.Source(sfd => null);
+
+			var searchRequest = selector.Invoke(new SearchDescriptor<SampleDomainObject>());
+			var query = searchRequest.Query as IQueryContainer;
+
+			// this is fine
+			query.Bool.Must.Should().NotBeEmpty();
+			query.Bool.Must.First().Should().NotBeNull("Must");
+
+			// this too...
+			query.Bool.MustNot.Should().NotBeEmpty();
+			// ... but this is fails as the collection contains one `<null>` entry which explains why it's missing from the serialized request JSON
+			query.Bool.MustNot.First().Should().NotBeNull("MustNot");
+		}
+
+		[U]
+		public void GithubIssue281_MustNotTermQueryAndNonEmptyValueShouldBeRegisteredAsNonNull()
+		{
+			Func<SearchDescriptor<SampleDomainObject>, ISearchRequest> selector = s => s
+				.Query(q => q
+					.Bool(b => b
+						.Must(m => m.Exists(e => e.Field("last_name")))
+						.MustNot(m => m.Term(t => t.Field("last_name.keyword").Value("mal")))
+					)
+				)
+				.Index("index")
+				.Source(sfd => null);
+
+			var searchRequest = selector.Invoke(new SearchDescriptor<SampleDomainObject>());
+			var query = searchRequest.Query as IQueryContainer;
+
+			// this is fine
+			query.Bool.Must.Should().NotBeEmpty();
+			query.Bool.Must.First().Should().NotBeNull("Must");
+
+			// this too...
+			query.Bool.MustNot.Should().NotBeEmpty();
+			// and so is this when the Term value is non-empty
+			query.Bool.MustNot.First().Should().NotBeNull("MustNot");
+		}
+
+		[U]
+		public void GithubIssue281_MustNotExistsClauseShouldNotBeNull()
+		{
+			Func<SearchDescriptor<SampleDomainObject>, ISearchRequest> selector = s => s
+				.Query(q => q
+					.Bool(b => b
+						.Must(m => m.Exists(e => e.Field("last_name")))
+						.MustNot(m => m.Exists(e => e.Field("last_name")))
+					)
+				)
+				.Index("index")
+				.Source(sfd => null);
+
+			var searchRequest = selector.Invoke(new SearchDescriptor<SampleDomainObject>());
+			var query = searchRequest.Query as IQueryContainer;
+
+			// this is fine
+			query.Bool.Must.Should().NotBeEmpty();
+			query.Bool.Must.First().Should().NotBeNull("Must");
+
+			// MustNot ... Exists seems to work
+			query.Bool.MustNot.Should().NotBeEmpty();
+			query.Bool.MustNot.First().Should().NotBeNull("MustNot");
+		}
+
+		[U]
+		public void GithubIssue281_TermQueryWithNonEmptyValueSerializesToNonNullResult()
+		{
+			Func<QueryContainerDescriptor<SampleDomainObject>, QueryContainer> termQuery =
+				m => m.Term(t => t.Field("last_name.keyword").Value("doe"));
+
+			var result = termQuery.Invoke(new QueryContainerDescriptor<SampleDomainObject>());
+
+			result.Should().NotBeNull();
+		}
+
+		[U]
+		public void GithubIssue281_TermQueryWithEmptyValueSerializesToNonNullResult()
+		{
+			Func<QueryContainerDescriptor<SampleDomainObject>, QueryContainer> termQuery =
+				m => m.Term(t => t.Field("last_name.keyword").Value(string.Empty));
+
+			var result = termQuery.Invoke(new QueryContainerDescriptor<SampleDomainObject>());
+
+			result.Should().NotBeNull();
+		}
+
+		[TU]
+		[InlineData("null", null, true)]
+		[InlineData("non-empty string", "doe", false)]
+		[InlineData("empty string", "", false)]
+		public void GithubIssue281_TermQueryIsConditionless(string scenario, string val, bool expected)
+		{
+			bool SimulateIsConditionless(ITermQuery q)
+			{
+				return q.Value == null || string.IsNullOrEmpty(q.Value.ToString());
+			}
+
+			var temrQuery = new TermQuery { Value = val };
+
+			var result = SimulateIsConditionless(temrQuery);
+
+			result.Should().Be(expected, $"{scenario} should be conditionless: ${expected}");
+		}
+	}
+}