How to Mock Elasticsearch NEST's IGetMappingResponse for Unit Testing

With Nkosi's help I found that TypeMappings has an internal constructor. Knowing that, I created an instance of TypeMappings using Reflection. Here is the code I used to create the object.

IReadOnlyDictionary<TypeName, TypeMapping> backingDictionary = new ReadOnlyDictionary<TypeName, TypeMapping>(new Dictionary<TypeName, TypeMapping>        {            [typeName.Name] = typeMapping        });                   Type[] typeMappingsArgs = new Type[] { typeof(IConnectionConfigurationValues), typeof(IReadOnlyDictionary<TypeName, TypeMapping>) };        object[] typeMappingsInputParams = new object[] { elasticClient.ConnectionSettings, backingDictionary };        TypeMappings typeMappings = (TypeMappings)typeof(TypeMappings).GetConstructor(              BindingFlags.NonPublic | BindingFlags.Instance,              null, typeMappingsArgs, null).Invoke(typeMappingsInputParams);

Here is the code for creating my mocked IGetMappingResponse. I used FakeItEasy to insert some information.

private Nest.IGetMappingResponse GetFakeMappingResponse(Nest.IElasticClient elasticClient)    {        var fieldName = "fieldName";        var indexName = "indexName";        var documentTypeName = "documentTypeName";        var typeMapping = new TypeMapping();        var properties = new Properties();        typeMapping.Properties = properties;        var property = new TextProperty();        property.Name = fieldName;                    PropertyName propertyName = new PropertyName(fieldName);        typeMapping.Properties.Add(propertyName, property);        Type[] typeNameArgs = new Type[] { typeof(string) };        object[] typeNameInputParams = new object[] { documentTypeName };        TypeName typeName = (TypeName)typeof(TypeName).GetConstructor(              BindingFlags.NonPublic | BindingFlags.Instance,              null, typeNameArgs, null).Invoke(typeNameInputParams);        IReadOnlyDictionary<TypeName, TypeMapping> backingDictionary = new ReadOnlyDictionary<TypeName, TypeMapping>(new Dictionary<TypeName, TypeMapping>        {            [typeName.Name] = typeMapping        });                   Type[] typeMappingsArgs = new Type[] { typeof(IConnectionConfigurationValues), typeof(IReadOnlyDictionary<TypeName, TypeMapping>) };        object[] typeMappingsInputParams = new object[] { elasticClient.ConnectionSettings, backingDictionary };        TypeMappings typeMappings = (TypeMappings)typeof(TypeMappings).GetConstructor(              BindingFlags.NonPublic | BindingFlags.Instance,              null, typeMappingsArgs, null).Invoke(typeMappingsInputParams);        IndexMappings indexMappings = new IndexMappings();        typeof(IndexMappings).GetProperty("Mappings", BindingFlags.Public | BindingFlags.Instance).SetValue(indexMappings, typeMappings);        ReadOnlyDictionary<Nest.IndexName, Nest.IndexMappings> indices = new ReadOnlyDictionary<Nest.IndexName, Nest.IndexMappings>(new Dictionary<Nest.IndexName, Nest.IndexMappings>        {            [indexName] = indexMappings        });        var fakeMappingResponse = A.Fake<IGetMappingResponse>();        A.CallTo(() => fakeMappingResponse.ServerError).Returns(null);        A.CallTo(() => fakeMappingResponse.IsValid).Returns(true);        A.CallTo(() => fakeMappingResponse.Indices).Returns(indices);        return fakeMappingResponse;    }