Question

I’m trying to mock (using Rhino.Mocks) a DataService which returns an IDataReader. I Can mock the IDataReader (StackOverFlow Q 1792984) but if I then Stub out A Data Service which returns this DataReader and inject it into the method I am trying to test it the stub returns only a null Data Reader.

IDataService

public interface IDataService
{
 SqlDataReader ExecuteReader(string cmdText, CommandType commandType);
 <rest of definition ommited
}

Unit test

    [TestMethod]
    public void GetCustomer_Pass()
    {
        //Arrange
        var customer = new Customer()
                       {
                         Id = 1, FirstName = "Patrick",
                         LastName = "Hastings", ProfilePictureURL = ""
                       };

        var mockDataService = MockRepository.GenerateStub<IDataService>();

        var reader = MockRepository.GenerateStub<IDataReader>();
        reader.Stub(x => x.Read()).Repeat.Once().Return(true);
        reader.Stub(x => x.Read()).Return(false);
        reader.Stub(x => x["Id"]).Return(customer.Id);
        reader.Stub(x => x["FirstName"]).Return(customer.FirstName);
        reader.Stub(x => x["LastName"]).Return(customer.LastName);
        reader.Stub(x => x["ProfilePictureURL"]).Return(customer.ProfilePictureURL);

        mockDataService.Stub( s =>
            s.ExecuteReader(string.Format("select FirstName, LastName,ProfilePictureURL from customer where Id = {0}", customer.Id),
                            CommandType.Text))
                            .Return(reader as SqlDataReader);

        var custRepository = new CustomerRepository(mockDataService);

        //Act
        var customer2 = custRepository.GetCustomer(1);
        //Assert
        Assert.AreEqual(customer.FirstName, customer2.FirstName,"FirstName Mismatch");
        Assert.AreEqual(customer.LastName, customer2.LastName, "LastName Mismatch");
    }

Method UnderTest

    public CustomerRepository(IDataService dataService) //Constructor
    {
        if (dataService == null) throw new ArgumentNullException("dataService", "dataService cannot be null.");
        this.dataService = dataService;
    }

    public Customer GetCustomer(int id)
    {
        var sql =string.Format("select FirstName, LastName, ProfilePictureURL from customer where Id = {0}",id);
        var dr = dataService.ExecuteReader(sql, CommandType.Text);
        Customer customer ;
        using (dr)
        {
            if (!dr.Read()){return null;}
            customer = new Customer
                         {
                             FirstName = dr["FirstName"].ToString(),
                             LastName = dr["LastName"].ToString(),
                             ProfilePictureURL = dr["ProfilePictureURL"].ToString()
                         };
        }
        return customer;
    }

This issue that I get is that when “dataService.ExecuteReader(sql, CommandType.Text);” should return the mocked IDataReader but instead returns Null – any pointers as to what I am doing wrong would be gratefully appreciated.

Answer 1

First point:

I believe because of different arguments passed into the ExecuteReader() method:

Set in expectation:

"select FirstName, LastName,ProfilePictureURL...

Passed whilst actual call: (extra space between comma and ProfilePictureURL)

"select FirstName, LastName, ProfilePictureURL...

Sometimes IgnoreArguments() is pretty useful when argument itself does not matter

Second Point:

.Return(reader as SqlDataReader);

This is invalid cast because reader is a mock object created by RhinoMock.

I believe you do not need a SqlDataReader type so just return reader itself

 .Return(reader)

PS: Also I would suggest store values which are repeating as constants, you can store customerId = 1 as constant as well to avoid such possible issues.