How do I unit test errors in an IDataErrorInfo business object?

Question

I am writing (attempting to write) unit tests for a WPF application.

The business objects that the UI binds to implement IDataErrorInfo, such that when I set ValidatesOnDataErrors=True in my View xaml, the error indexer (this[]) is called anytime the setter for the bound business object is called. That part is great.

Now if I call that same property's setter from a unitTest, it never calls the error indexer. How do I force the IDataErrorInfo indexer to be evaluated from within a unit test?

just for illustration, here is one of my simple error indexers that contains a Name property. Setting 'myObject.Name = string.Empty;' does call the setter, but not the error indexer when I do this in my unit tests.

        public string Name
    {
        get { return _name; }
        set
        {
            _name = value;
            IsDirty = true;
            OnPropertyChanged("Name");
        }
    }

        #region IDataErrorInfo

    public Dictionary<string, string> ErrorCollection;

    public string this[string property]
    {
        get
        {
            string msg = null;
            switch (property)
            {
                case "Name":
                    if (string.IsNullOrEmpty(Name))
                        msg = "ICU Name is required.";
                    else if (Name.Length < 4)
                        msg = "ICU Name must contain at least 4 characters.";
                    else if (_parent.Units.AsEnumerable().Count(u => u.Name == Name) > 1)
                        msg = Name + " already exists, please change to a different Name.";
                    break;
            }


            if (msg != null && !ErrorCollection.ContainsKey(property))
                ErrorCollection.Add(property, msg);
            if (msg == null && ErrorCollection.ContainsKey(property))
                ErrorCollection.Remove(property);

            return msg;
        }
    }

    public string Error
    {
        get { return null; }
    }
    #endregion

Thanks!

Answer 1

What I would do in a unit test is to set the value of Name, then explicitly call the indexer to check for the error.

You could hook the PropertyChanged event in the unit test, but I don't think it makes sense, as you'd then have to somehow notify the test method that the event was received and then you'd have to call the indexer anyway.