using Microsoft.EntityFrameworkCore;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;
using System.Collections.Generic;
using System.Linq;

...

        private static Mock<DbSet<T>> MockDbSet<T>(IEnumerable<T> ls) where T : class
        {
            var data = ls.AsQueryable();
            var mockSet = new Mock<DbSet<T>>();
            mockSet.As<IQueryable<T>>().Setup(m => m.Provider).Returns(data.Provider);
            mockSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(data.Expression);
            mockSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(data.ElementType);
            mockSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(
                () => data.GetEnumerator());
            return mockSet;
        }