Question

I am implementing a data store access classes for my WP7.1 application.

The general structure of inheritance of classes is the following:

IDataStore – interface that declears logical operations that the application doaim classes use.

abstract class XmlDataStore implements the requesired by the interface functionality via XElement routines, but leaves the base data store configuration to the successor classes.

The abstract methods in XmlDataStore are:

public abstract void CreateDataStore();

public abstract void OpenDataStore();

public abstract void SaveChanges();

Also, an abstract class contains the const strings definitions thare used by successors:

protected const string xmlRoot = "Data";
protected const string booksRoot = "Records";
protected const string settingsRoot = "Settings";

There are two successors to XmlDataStore: IsolatedStorageDataStore and InMemoryDataStore.

The later was created for test purposes, so I can test the correcness of the xml-manipulation routines implemented in abstract XmlDataStore.

I have added a Windows Phone Class Library to my solution. References NUnit via NuGet and have implemented one [TestFixture]:

[TestFixture]
public class XmlDataStoreTest
{
        private IDataStore _store;

        public XmlBookProgressStoreTest()
        {
            _store = new InMemoryXmlDataStore();
        }

        [Test]
        public void TestRegisterBookView()
        {
            _store.RegisterBookView(BookId, "TestBook");
        }
}

An InMemoryDataStore currently is the following class:

public class InMemoryDataStore : XmlDataStore
    {
        private XDocument _inMemDoc;

        public InMemoryDataStore()
        {
            CreateDataStore();
            OpenDataStore();
        }

        public override void CreateDataStore()
        {
            try
            {
                var root = new XElement(xmlRoot);
                root.Add(new XElement(booksRoot));
                root.Add(new XElement(settingsRoot));

                _inMemDoc = new XDocument(root);
            }
            catch (Exception ex)
            {
                throw ex;
            }

        }

        public override void OpenDataStore()
        {
            _deusBookDataFile = _inMemDoc;
        }

        public override void SaveChanges()
        {}
    }
}

Now, when I debug this class in a simple application debug, the InMemoryDataStore instanciates fine, but when I debug my unit test, I get a DivideByZeroExceptionin this line of code: var root = new XElement(xmlRoot);

Clearly the problem only happens in unit test execution so it must be somehow connected to it. Why is the exception there and how can I fix it?

Answer 1

As of now, this is a common problem. For Unit Testing Silverlight apps one should currently use Silverlight Testing Framework and see the results of the tests on the device’s screen.

Things should change with the release of NUnit 3 which is to feature a Silverlight support.