public void TestConcatOperator()
        {
            EntityCollection<TestAccountEntity> entities = new EntityCollection<TestAccountEntity>();
            entities.Add(new TestAccountEntity(100, 5));
            entities.Add(new TestAccountEntity(102, 8));

            EntityCollection<TestAccountEntity> entities0 = new EntityCollection<TestAccountEntity>();
            entities0.Add(new TestAccountEntity(103, 15));
            entities0.Add(new TestAccountEntity(104, 2));

            IEnumerable<TestAccountEntity> result = entities.Concat(entities0);

            Assert.IsNotNull(result);
            foreach (TestAccountEntity entity in result)
            {
                Assert.IsNotNull(entity);
                Console.WriteLine(entity);
            }
        }