单元测试 mock EF 中DbContext 和DbSet

现在EF越来越流行了，很多时候业务成都是直接访问DbContext 和DbSet来操作数据的。 那么我们测试的时候如何来mock这2个对象了？现在时间很晚了， 就直接贴code吧：首先建一个帮助类：

 public class MockedDbContext<T> : Mock<T> where T : DbContext
    {
        public Dictionary<string, object> Tables
        {
            get { return _Tables ?? (_Tables = new Dictionary<string, object>()); }
        }
        private Dictionary<string, object> _Tables;

    }
    public static class EntityFrameworkMockHelper
    {
        /// <summary>
        /// Returns a mock of a DbContext
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <returns></returns>
        public static MockedDbContext<T> GetMockContext<T>() where T : DbContext
        {
            var instance = new MockedDbContext<T>();
            instance.MockTables();
            return instance;
        }

        /// <summary>
        /// Use this method to mock a table, which is a DbSet{T} oject, in Entity Framework.
        /// Leave the second list null if no adds or deletes are used.
        /// </summary>
        /// <typeparam name="T">The table data type</typeparam>
        /// <param name="table">A List{T} that is being use to replace a database table.</param>
        /// <returns></returns>
        public static DbSet<T> MockDbSet<T>(List<T> table) where T : class
        {
            var dbSet = new Mock<DbSet<T>>();
            dbSet.As<IQueryable<T>>().Setup(q => q.Provider).Returns(() => table.AsQueryable().Provider);
            dbSet.As<IQueryable<T>>().Setup(q => q.Expression).Returns(() => table.AsQueryable().Expression);
            dbSet.As<IQueryable<T>>().Setup(q => q.ElementType).Returns(() => table.AsQueryable().ElementType);
            dbSet.As<IQueryable<T>>().Setup(q => q.GetEnumerator()).Returns(() => table.AsQueryable().GetEnumerator());
            dbSet.Setup(set => set.Add(It.IsAny<T>())).Callback<T>(table.Add);
            dbSet.Setup(set => set.AddRange(It.IsAny<IEnumerable<T>>())).Callback<IEnumerable<T>>(table.AddRange);
            dbSet.Setup(set => set.Remove(It.IsAny<T>())).Callback<T>(t => table.Remove(t));
            dbSet.Setup(set => set.RemoveRange(It.IsAny<IEnumerable<T>>())).Callback<IEnumerable<T>>(ts =>
            {
                foreach (var t in ts) { table.Remove(t); }
            });
            return dbSet.Object;
        }

        /// <summary>
        /// Mocks all the DbSet{T} properties that represent tables in a DbContext.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="mockedContext"></param>
        public static void MockTables<T>(this MockedDbContext<T> mockedContext) where T : DbContext
        {
            Type contextType = typeof(T);
            var dbSetProperties = contextType.GetProperties().Where(prop => (prop.PropertyType.IsGenericType) && prop.PropertyType.GetGenericTypeDefinition() == typeof(DbSet<>));
            foreach (var prop in dbSetProperties)
            {
                var dbSetGenericType = prop.PropertyType.GetGenericArguments()[0];
                Type listType = typeof(List<>).MakeGenericType(dbSetGenericType);
                var listForFakeTable = Activator.CreateInstance(listType);
                var parameter = Expression.Parameter(contextType);
                var body = Expression.PropertyOrField(parameter, prop.Name);
                var lambdaExpression = Expression.Lambda<Func<T, object>>(body, parameter);
                var method = typeof(EntityFrameworkMockHelper).GetMethod("MockDbSet").MakeGenericMethod(dbSetGenericType);
                mockedContext.Setup(lambdaExpression).Returns(method.Invoke(null, new[] { listForFakeTable }));
                mockedContext.Tables.Add(prop.Name, listForFakeTable);
            }
        }

    }

再来看看的我们DbContext的类吧：

 public class BloggerEntities : DbContext
    {
        public BloggerEntities()
            : base("BloggerEntities")
        {
            Configuration.ProxyCreationEnabled = false;
        }

        public virtual DbSet<Blog> Blogs { get; set; }
        public virtual DbSet<Article> Articles { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.Add(new ArticleConfiguration());
            modelBuilder.Configurations.Add(new BlogConfiguration());
        }
    }

public virtual DbSet<Blog> Blogs { get; set; }

public virtual DbSet<Article> Articles { get; set; }

注意了，我一般DbSet属性是没有添加virtual， 结果上面的 mockedContext.Setup(lambdaExpression).Returns(method.Invoke(null, new[] { listForFakeTable }));这句一直报错，搞了我2个小时都没有搞定。不能mock 实例方法。

单元测试code：

  static void Main(string[] args)
        {
            var context = EntityFrameworkMockHelper.GetMockContext<BloggerEntities>().Object;
            context.Articles.Add(new Article
            {
                Author = "Gavin",
                BlogID = 1,
                Contents = "test",
                ID = 2,
                Title = "test title",
                URL = "article URL"
            });
            List<Blog> blogs = new List<Blog> {
            new Blog
            {
                ID = 1,
                URL = "blog url",
                Name = "blogs name"
            },
            new Blog
            {
                ID = 1,
                URL = "blog url",
                Name = "blogs name2222"
            }
             };

            //add
            context.Blogs.AddRange(blogs);
            //query
            var query1 = (from a in context.Articles
                          join b in context.Blogs on a.BlogID equals b.ID
                          select new { Author = a.Author, BlogName = b.Name }).ToList();
            //remove
            var blog = context.Blogs.FirstOrDefault(x => x.Name == "blogs name2222");
            context.Blogs.Remove(blog);
            //update
            context.Articles.FirstOrDefault(x=>x.ID==2).URL = "updated url";
            var query2 = (from a in context.Articles
                          join b in context.Blogs on a.BlogID equals b.ID
                          select new { Author = a.Author, ArticleUrl = a.URL }).ToList();

        }

参考：

Testing
with a mocking framework (EF6 onwards)

How
to mock an Entity Framework DbContext and its DbSet properties

文件下载地址：http://download.csdn.net/detail/dz45693/9514948