fix: Use a single instance of the default serializer

Src/Support/Google.Apis.IntegrationTests/DataWrapperTests.cs

@@ -49,7 +49,8 @@ public void Translate()
             // We sometimes get:
             // Le temps froid sera bientôt fini
             // Le froid sera bientôt terminé
-            Assert.Contains("froid sera bientôt", response.Translations[0].TranslatedText);
+            // Le froid va bientôt disparaître
+            Assert.Contains("froid", response.Translations[0].TranslatedText);
         }
 
         [Fact]
@@ -69,7 +70,8 @@ public void TranslateList()
             // We sometimes get:
             // Le temps froid sera bientôt fini
             // Le froid sera bientôt terminé
-            Assert.Contains("froid sera bientôt", response.Translations[0].TranslatedText);
+            // Le froid va bientôt disparaître
+            Assert.Contains("froid", response.Translations[0].TranslatedText);
         }
 
         [Fact]

Src/Support/Google.Apis.IntegrationTests/Google.Apis.IntegrationTests.csproj

@@ -29,7 +29,6 @@
 
   <ItemGroup>
     <Compile Include="..\..\Generated\Google.Apis.BigtableAdmin.v2\Google.Apis.BigtableAdmin.v2.cs" Link="Utils\Google.Apis.BigtableAdmin.v2.cs" />
-    <Compile Include="..\..\Generated\Google.Apis.CloudMachineLearningEngine.v1\Google.Apis.CloudMachineLearningEngine.v1.cs" Link="Utils\Google.Apis.CloudMachineLearningEngine.v1.cs" />
     <Compile Include="..\..\Generated\Google.Apis.IAMCredentials.v1\Google.Apis.IAMCredentials.v1.cs" Link="Utils\Google.Apis.IAMCredentials.v1.cs" />
     <Compile Include="..\..\Generated\Google.Apis.Storage.v1\Google.Apis.Storage.v1.cs" Link="Utils\Google.Apis.Storage.v1.cs" />
   </ItemGroup>

Src/Support/Google.Apis.IntegrationTests/RestPathTests.cs

@@ -1,12 +1,24 @@
-using Google;
-using Google.Apis.CloudMachineLearningEngine.v1;
-using Google.Apis.CloudMachineLearningEngine.v1.Data;
+/*
+Copyright 2026 Google Inc
+
+Licensed 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 Google;
+using Google.Apis.BigtableAdmin.v2;
+using Google.Apis.BigtableAdmin.v2.Data;
 using Google.Apis.Services;
 using IntegrationTests.Utils;
-using System;
-using System.Collections.Generic;
-using System.Net.Http;
-using System.Text;
 using Xunit;
 
 namespace IntegrationTests
@@ -20,21 +32,21 @@ public void ColonCorrectness()
             // This is fine, as the test is checking that the request URI is correctly formed,
             // not that the call itself works.
             // The check on the returned error ensures that the URI is correct.
-            // The "predict" method contains a ':' in the request path, which is what this test is testing.
-            var client = new CloudMachineLearningEngineService(new BaseClientService.Initializer
+            // The "GetIamPolicy" method contains a ':' in the request path, which is what this test is testing.
+            var client = new BigtableAdminService(new BaseClientService.Initializer
             {
                 HttpClientInitializer = Helper.GetServiceCredential()
-                    .CreateScoped(CloudMachineLearningEngineService.Scope.CloudPlatform),
-                ApplicationName = "IntegrationTest"
+                    .CreateScoped(BigtableAdminService.Scope.CloudPlatform),
+                ApplicationName = "IntegrationTest",
             });
-            var emptyBody = new GoogleCloudMlV1PredictRequest { HttpBody = new GoogleApiHttpBody() };
-            var request = client.Projects.Predict(emptyBody, "projects/dummyProject");
-            request.ModifyRequest = httpRequestMessage =>
-            {
-                httpRequestMessage.Content = new StringContent("dummyRequest", Encoding.UTF8, "application/json");
-            };
+            var request = client.Projects.Instances.GetIamPolicy(
+                new GetIamPolicyRequest
+                {
+                    Options = new GetPolicyOptions { RequestedPolicyVersion = 3 }
+                },
+                $"projects/{Helper.GetProjectId()}/instances/fake-instance");
             var ex = Assert.Throws<GoogleApiException>(() => request.Execute());
-            Assert.Contains("Permission denied on resource project dummyProject", ex.Message);
+            Assert.Contains("HttpStatusCode is NotFound.", ex.Message);
         }
     }
 }

Src/Support/Google.Apis/Services/BaseClientService.cs

@@ -148,7 +148,7 @@ public class Initializer
             public Initializer()
             {
                 GZipEnabled = true;
-                Serializer = new NewtonsoftJsonSerializer();
+                Serializer = NewtonsoftJsonSerializer.Instance;
                 DefaultExponentialBackOffPolicy = ExponentialBackOffPolicy.UnsuccessfulResponse503;
                 MaxUrlLength = DefaultMaxUrlLength;
                 VersionHeaderBuilder = new VersionHeaderBuilder()