C# – Entity Framework Core does not contain a definition for ‘Include’

I am trying to work with Entity Framework Core 1.0 and trying to utilize the .Include when filling objects through the dbcontext.

        EFTestContext context = new EFTestContext();
        var testEntity = context.TestEntity
            .Include(t => t.TestEntity2)
            .ToList();

It give me the error

does not contain a definition for 'Include' and no extension method 'Include' accepting a first argument of type 'DbSet' could be found

The only similar thing I found so far in Stackoverflow is

IQueryable<T> does not contain a definition for 'Include' and no extension method 'Include'

But adding the using statement

using System.Data.Entity;

Just give me the error

The type or namespace name 'Entity' does not exist in the namespace 'System.Data' (are you missing an assembly reference?)

Anyone know what I need to get the Include to show up with WF Core 1.0?