How do I mock the DocumentClientException that the Azure DocumentDB client library throws?

Hi,

 We are porting an existing .Net 452 application which uses the Microsoft.Azure.DocumentDB package to ASP .Net Core.

 In the existing version we were using the approach mentioned @ http://stackoverflow.com/questions/35618723/how-do-i-mock-the-documentclientexception-that-the-azure-documentdb-client-libra to Mock the DocumentClientException  class for unit testing since DocumentClientException does not have a public constructor. 

    private static DocumentClientException CreateDocumentClientExceptionForTesting(
                                           Error error, HttpStatusCode httpStatusCode)
    {
        var type = typeof (DocumentClientException);

        // we are using the overload with 3 parameters (error, responseheaders, statuscode)
       // use any one appropriate for you.

        var documentClientExceptionInstance = type.Assembly.CreateInstance(type.FullName,
            false, BindingFlags.Instance | BindingFlags.NonPublic, null,
            new object[] {error, (HttpResponseHeaders) null, httpStatusCode}, null, null);

        return (DocumentClientException)documentClientExceptionInstance;
    }

  Now, when we move to ASP .Net Core, this approach also does not work. The Assembly class has only two overloaded CreateInstance() methods.

        public object CreateInstance(string typeName);
        public object CreateInstance(string typeName, bool ignoreCase);

 The one is missing the CreateInstance() with the parameter of the arguments to the constructor and hence we cannot create the DocumentClientException instance for Unit Testing.

// The missing method in ASP .Net Core
        public virtual object CreateInstance(string typeName, bool ignoreCase, BindingFlags bindingAttr, Binder binder, object[] args, CultureInfo culture, object[] activationAttributes);

  Why is this CreateInstance() method removed? How can I create Mock objects for such classes through reflection when there is no default constructor available?

Thanks,

Ranjith