Why doesn't my unit test of my Silverlight XAML bindings work?

I have the following combo box:

<ComboBox x:Name="cmbCurrency" 
          ItemsSource="{Binding IsoCurrenciesList}"
          DisplayMemberPath="Description"
          SelectedValuePath="LocaleID"
          SelectedValue="{Binding CurrencyId, Mode=TwoWay">
</ComboBox>

Where IsoCurrenciesList- this IEnumerable<IsoCurrency>is the type defined by us and declared in the view model, as:

private IEnumerable<IsoCurrency> isoCurrenciesList;
public IEnumerable<IsoCurrency> IsoCurrenciesList
{
    get { return isoCurrenciesList; }
    set
    {
        isoCurrenciesList = value;
        RaisePropertyChangedEvent("IsoCurrenciesList");
    }
}

My unit test creates an instance of the view model and the view and sets some dummy currency data in a local list:

[TestInitialize]
public void TestInit()
{
    _target = new View();

    _viewModel = new ViewModel();

    var ukp = new IsoCurrency { Code = "GBP", Description = "Pound Sterling", LocaleID = 826 };
    var usd = new IsoCurrency { Code = "USD", Description = "US Dollar", LocaleID = 840 };
    var eur = new IsoCurrency { Code = "EUR", Description = "Euro", LocaleID = 978 };
    _currencies = new List<IsoCurrency> { ukp, usd, eur };

    GetUIElement<Grid>("LayoutRoot").DataContext = _viewModel;
}

private T GetUIElement<T>(string name) where T : UIElement
{
    return (T)_target.FindName(name);
}

Then the verification method is called. This should set the currency ComboBox.Items(through the property ItemsSource)

[Asynchronous]
[TestMethod]
public void TestCurrencySelection()
{
    _target.Loaded += (s, e) =>
        {
            // Set the currency list explicitly
            _viewModel.IsoCurrenciesList = _currencies;

            var currencyCombo = GetUIElement<ComboBox>("cmbCurrency");
            // This assert fails as Items.Count == 0
            CollectionAssert.AreEquivalent(currencyCombo.Items, _currencies, "Failed to data-bind currencies.");

            EnqueueTestComplete();
        };

    TestPanel.Children.Add(_target);
}

I followed the recommendations on Jeremy Likeness's blog , but I can't pass the binding test.

I tried to check the bindings of other properties - simple strings, logical and integers, but the changes made from both ends do not affect the other.

, , , TestPanel "" , , .

UPDATE

, . ( , ), , , , .. - , XAML , DataContext. , () .

, . XAML :

<Grid x:Name="LayoutRoot">
    <VisualStateManager.VisualStateGroups>
        ...
    </VisualStateManager.VisualStateGroups>

    <toolkit:BusyIndicator x:Name="activityControl" 
                           IsBusy="{Binding IsBusy}" 
                           BusyContent="{Binding BusyContent}" >
        <Grid>
            ... The page definition including sub grids, stack panels
                and the combo box I'm testing along with other controls

            <ops:SaveConfirmation Grid.Row="1" Margin="5"
                                  x:Name="saveConfirmation"
                                  SavedState="{Binding VendorSaved, Mode=TwoWay}" />
        </Grid>
    </toolkit:BusyIndicator/>
</Grid>

BusyIndicator - Silverlight Toolkit, SaveConfirmation - , .

IsBusy BusyIndicator, , . , SavedState SaveConfirmation, - VendorSaved true , , bound false.

var busyIndicator = GetUIElement<BusyIndicator>("activityControl");
Assert.AreEqual(busyIndicator.IsBusy, _viewModel.IsBusy, "Failed to data-bind busy indicator.");

var saveConfirmation = GetUIElement<SaveConfirmation>("saveConfirmation");
Assert.AreEqual(saveConfirmation.SavedState, _viewModel.VendorSaved, "Failed to data-bind saved state");

, , .

, ?