Class VisibleForTestOnly (1.55.0) 

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method | AttributeTargets.Property | AttributeTargets.Field)]
public class VisibleForTestOnly : Attribute

Marker Attribute to indicate a Method/Class/Property has been made more visible for purpose of testing. Mark the member as internal and make the testing assembly a friend using

[assembly: InternalsVisibleTo("Full.Name.Of.Testing.Assembly")]

Inheritance

Object > Attribute > VisibleForTestOnly

Namespace

Google.Apis.Testing

Assembly

Google.Apis.Core.dll

Extension Method