<PackageReference Include="NUnit" Version="4.3.2" />

NUnit.Compatibility.AttributeHelper

public static class AttributeHelper
Provides a platform-independent methods for getting attributes for use by AttributeConstraint and AttributeExistsConstraint.
namespace NUnit.Compatibility { public static class AttributeHelper { public static Attribute[] GetCustomAttributes(object actual, Type attributeType, bool inherit); } }