Entity Framework Core example using an InMemoryDatabse along with xUnit.

Tests.cs

using System.Linq;
using Data;
using Microsoft.EntityFrameworkCore;
using Xunit;

namespace Tests
{
    public class UserContextTests
    {
        public UserContextTests()
        {
        }

        [Fact]
        public void WhenUserIsInsertedItCanBeSelected() 
        {
            var user = new User
            {
                Id = 1,
                FirstName = "Hello",
                LastName = "World"
            };
            var sut = GetInstance();

            sut.Users.Add(user);
            sut.SaveChanges();

            var retrieved = sut.Users.First();
            Assert.Equal(user, retrieved);
        }

        [Fact]
        public void GivenContextItMustBeEmpty()
        {
            var sut = GetInstance();
            Assert.Equal(0, sut.Users.Count());
        }

        private UserContext GetInstance()
        {
            var builder = new DbContextOptionsBuilder<UserContext>();
            builder.UseInMemoryDatabase();
            var context = new UserContext(builder.Options);
            context.Database.EnsureDeleted();  // as if having to have a method like this was not lame enough
            return context;
        }
    }
}

User.cs

namespace Data
{
    public class User
    {
        public int Id { get; set; }
 
        public string FirstName { get; set; }
 
        public string LastName { get; set; }
    }
}

UserContext.cs

using Microsoft.EntityFrameworkCore;
 
namespace Data
{
    public class UserContext : DbContext
    {
        public UserContext(DbContextOptions<UserContext> options)
            : base(options)
        {
        }

        protected override void OnConfiguring(DbContextOptionsBuilder options)
        {
            options.UseInMemoryDatabase();
        }
 
        public DbSet<User> Users { get; set; }
    }
}