How to mock datacontext (LINQToSQL) which is part of another assembly?

I am using LinqToSQL in my project.As pert of my unit testing, I am trying to mock datacontext which is part of another assembly which is referenced in the ASP.NET WEB API project.

Based on the following URL: http://ift.tt/1P8FKWb

I tried to create a partial class for the datacontext but somehow it is not working.

Can anyone help me to know how to mock the datacontext class which is part of another referenced assembly.