How to mock an SqlDataReader using Moq - Update

Question

Hi,

I'm new to moq and setting up mocks so i could do with a little help.

Title says it all really - how do I mock up an SqlDataReader using Moq?

Thanks

Update

After further testing this is what I have so far:

private IDataReader MockIDataReader()
{
    var moq = new Mock<IDataReader>();
    moq.Setup( x => x.Read() ).Returns( true );
    moq.Setup( x => x.Read() ).Returns( false );
    moq.SetupGet<object>( x => x["Char"] ).Returns( 'C' );

    return moq.Object;
}

private class TestData
{
    public char ValidChar { get; set; }
}

private TestData GetTestData()
{
   var testData = new TestData();

   using ( var reader = MockIDataReader() )
   {
       while ( reader.Read() )
       {
           testData = new TestData
           {
               ValidChar = reader.GetChar( "Char" ).Value
           };
       }
   }

   return testData;
}

The issue you is when I do reader.Read in my GetTestData() method its always empty. I need to know how to do something like

reader.Stub( x => x.Read() ).Repeat.Once().Return( true ) 

as per the rhino mock example: http://stackoverflow.com/questions/1792984/mocking-a-datareader-and-getting-a-rhino-mocks-exceptions-expectationviolationexc

Answer 1

I have no experience in mocking the SqlDataReader but, if you can, you should mock the interface. I've looked it up for you and maybe this article could help ya :] http://stackoverflow.com/questions/1792984/mocking-a-datareader-and-getting-a-rhino-mocks-exceptions-expectationviolationexc It uses Rhinomocks but the idea is the same. Suggested there, you should Mock IDataReader. When you've mocked that, you shouldn't have problems doing .Setups() on the mock ^^

If you've already tried mocking an interface, maybe you could show us where you get stuck by posting some example code :]

Answer 2

After some testing the problem is trying to set the DataReader.Read() to true for one loop and then setting it to false. Rhino Mock has the Repeat.Once() option but I could not find a similar method in Moq (I might be wrong here).

The main reason for testing this was the extension methods to convert the reader to the relevant datatype so in the end I removed the while loop and just accessed the values that had been setup in my mock. The code looks as follows:

private IDataReader MockIDataReader()
{
    var moq = new Mock<IDataReader>();
    moq.SetupGet<object>( x => x["Char"] ).Returns( 'C' );

    return moq.Object;
}

private class TestData
{
    public char ValidChar { get; set; }
}

private TestData GetTestData()
{
    var testData = new TestData();

    using ( var reader = MockIDataReader() )
    {
       testData = new TestData
       {
           ValidChar = reader.GetChar( "Char" ).Value
       };
   }

   return testData;
}

Not an ideal solution but it works. If anyone knows better leave a comment thanks.

Answer 3

Moq has an ability to run some code after the method is executed. It is called "Callback". Modify your code this way and it will work:

private IDataReader MockIDataReader()
{
    var moq = new Mock<IDataReader>();

    bool readToggle = true;

    moq.Setup(x => x.Read())
         // Returns value of local variable 'readToggle' (note that 
         // you must use lambda and not just .Returns(readToggle) 
         // because it will not be lazy initialized then)
        .Returns(() => readToggle) 
        // After 'Read()' is executed - we change 'readToggle' value 
        // so it will return false on next calls of 'Read()'
        .Callback(() => readToggle = false); 

    moq.Setup(x => x["Char"])
        .Returns('C');

    return moq.Object;
}

private class TestData
{
    public char ValidChar { get; set; }
}

private TestData GetTestData()
{
    var testData = new TestData();

    using ( var reader = MockIDataReader() )
    {
       testData = new TestData
       {
           ValidChar = (Char)reader["Char"]
       };
   }

   return testData;
}

But what if it will be required IDataReader to contain not only single row, but several? Well, here is a sample:

// You should pass here a list of test items, their data
// will be returned by IDataReader
private IDataReader MockIDataReader(List<TestData> ojectsToEmulate)
{
    var moq = new Mock<IDataReader>();

    // This var stores current position in 'ojectsToEmulate' list
    int count = -1;

    moq.Setup(x => x.Read())
        // Return 'True' while list still has an item
        .Returns(() => count < ojectsToEmulate.Count - 1)
        // Go to next position
        .Callback(() => count++);

    moq.Setup(x => x["Char"])
        // Again, use lazy initialization via lambda expression
        .Returns(() => ojectsToEmulate[count].ValidChar);

    return moq.Object;
}