I've created unit test for the "student" CRUD operations that looks like this:

    [Test]
        public void Can_Exec_CrudOps()
        {
            #region Prepare

            
            var account = Processor.Execute(new CreateAccount
            {
                Email = "[email protected]",
                Username = "username",
                Password = "password",
            }).Result;

            #endregion

            var student = Processor.Execute(new CreateStudent
            {
                AccountId = account.EntityID
            }).Result;

            Assert.NotNull(student);
            student.AreEqual(Processor.Execute(new GetStudent
            {
                EntityId = student.EntityID
            }).Result);
            student.AreEqual(Processor.Execute(new GetStudentByAccount
            {
                AccountId = account.EntityID
            }).Result);

            var upd_student = Processor.Execute(new UpdateStudent
            {
                EntityId = student.EntityID,
                Flags = StudentFlags.Active
            }).Result;

            Assert.NotNull(upd_student);
            upd_student.AreEqual(student);
            upd_student.Flags.AreEqual(StudentFlags.Active);

            Processor.Execute(new DeleteStudent
            {
                EntityId = student.EntityID
            });
        }

As you can see, the region #prepare contains code that will insert required data to the database for the current test to be possible. 

Is it good practice to create a single test for each CRUD operation and then call that test inside the tests that require them?

What I'm thinking about would look like this:

     [TestFixture]
    public class StudentTest : OperationTest
    {
        protected override IEnumerable<Type> ModelMappings
        {
            get
            {
                return NHMappings.EDUCATION;
            }
        }

        [Test]
        public void Can_Exec_CrudOps()
        {
            #region Prepare
            // here is what changed //
            var acc = new AccountTests();
            var acc_id=    acc.create_account();
          

            #endregion

            var student = Processor.Execute(new CreateStudent
            {
                            //here too//
                AccountId = acc_id
            }).Result;

            Assert.NotNull(student);
            student.AreEqual(Processor.Execute(new GetStudent
            {
                EntityId = student.EntityID
            }).Result);
            student.AreEqual(Processor.Execute(new GetStudentByAccount
            {
                            // and here//
                AccountId = acc_id
            }).Result);

            var upd_student = Processor.Execute(new UpdateStudent
            {
                EntityId = student.EntityID,
                Flags = StudentFlags.Active
            }).Result;

            Assert.NotNull(upd_student);
            upd_student.AreEqual(student);
            upd_student.Flags.AreEqual(StudentFlags.Active);

            Processor.Execute(new DeleteStudent
            {
                EntityId = student.EntityID
            });
            // and here //
            acc.deleteaccount(acc_id);
        }
    }

So the point is not to write the same code over and over again.