Unit testing a LINQ2SQL repository

Question

I am taking my first steps with MsTest and Moq and would like to unit test a Linq2SQL repository class. The problem is that I do not want the unit tests to permantly modify my development database.

Which would be the best approach for this scenario?

• Let each test operate on my real development database, but make sure each test cleans up after itself
• Create a duplicate of my development database and dbml for the unit test and use that context instead so I can clear the entire database before each test run
• Find some elaborate way of mocking the Datacontext (please bear in mind that I am a total Moq noob).
• Something completely different? Perhaps something that would automate setting up the database for me before each test run?

Edit: I just learned that MBUnit has a rollback attribute that reverses any database operations run by a test case. I am not particularly attached to MSTest, so could this be an easy answer to my problem?

Answer 1

I went with mocking/faking the database using some wrapper classes + a fake implementation based on http://andrewtokeley.net/archive/2008/07/06/mocking-linq-to-sql-datacontext.aspx. Note that I did end up implementing SubmitChanges logic in my fake data context wrapper to test out the validation logic in my entity's partial class implementation. I think that this was really the only tricky part which differed substantially from Tokeley's implementation.

I'll include my FakeDataContextWrapper implementation below:

public class FakeDataContextWrapper : IDataContextWrapper
{

    public DataContext Context
    {
        get { return null; }
    }

    private List<object> Added = new List<object>();
    private List<object> Deleted = new List<object>();

    private readonly IFakeDatabase mockDatabase;

    public FakeDataContextWrapper( IFakeDatabase database )
    {
        mockDatabase = database;
    }

    protected List<T> InternalTable<T>() where T : class
    {
        return (List<T>)mockDatabase.Tables[typeof( T )];
    }

    #region IDataContextWrapper Members

    public virtual IQueryable<T> Table<T>() where T : class
    {
        return mockDatabase.GetTable<T>();
    }

    public virtual ITable Table( Type type )
    {
        return new FakeTable( mockDatabase.Tables[type], type );
    }

    public virtual void DeleteAllOnSubmit<T>( IEnumerable<T> entities ) where T : class
    {
        foreach (var entity in entities)
        {
            DeleteOnSubmit( entity );
        }
    }

    public virtual void DeleteOnSubmit<T>( T entity ) where T : class
    {
        this.Deleted.Add( entity );
    }

    public virtual void InsertAllOnSubmit<T>( IEnumerable<T> entities ) where T : class
    {
        foreach (var entity in entities)
        {
            InsertOnSubmit( entity );
        }
    }

    public virtual void InsertOnSubmit<T>( T entity ) where T : class
    {
        this.Added.Add( entity );
    }

    public virtual void SubmitChanges()
    {
        this.SubmitChanges( ConflictMode.FailOnFirstConflict );
    }

    public virtual void SubmitChanges( ConflictMode failureMode )
    {
        try
        {
            foreach (object obj in this.Added)
            {
                MethodInfo validator = obj.GetType().GetMethod( "OnValidate", BindingFlags.Instance | BindingFlags.NonPublic );
                if (validator != null)
                {

                    validator.Invoke( obj, new object[] { ChangeAction.Insert } );
                }
                this.mockDatabase.Tables[obj.GetType()].Add( obj );
            }

            this.Added.Clear();

            foreach (object obj in this.Deleted)
            {
                MethodInfo validator = obj.GetType().GetMethod( "OnValidate", BindingFlags.Instance | BindingFlags.NonPublic );
                if (validator != null)
                {
                    validator.Invoke( obj, new object[] { ChangeAction.Delete } );
                }
                this.mockDatabase.Tables[obj.GetType()].Remove( obj );
            }

            this.Deleted.Clear();

            foreach (KeyValuePair<Type, IList> tablePair in this.mockDatabase.Tables)
            {
                MethodInfo validator = tablePair.Key.GetMethod( "OnValidate", BindingFlags.Instance | BindingFlags.NonPublic );
                if (validator != null)
                {
                    foreach (object obj in tablePair.Value)
                    {
                        validator.Invoke( obj, new object[] { ChangeAction.Update } );
                    }
                }
            }
        }
        catch (TargetInvocationException e)
        {
            throw e.InnerException;
        }
    }

    public void Dispose() { }

    #endregion
}