AutoFixture hint by moodmosaic on how to add ObservableCollection support (From AutoFixture issue https://github.com/AutoFixture/AutoFixture/issues/191#issuecomment-26084930)

AutoFixture_ObservableCollection

fixture.Customizations.Add(
    new FilteringSpecimenBuilder(
        new MethodInvoker(
            new EnumerableFavoringConstructorQuery()),
        new ObservableCollectionSpecification()));

internal class ObservableCollectionSpecification : IRequestSpecification
{
    public bool IsSatisfiedBy(object request)
    {
        var type = request as Type;
        if (type == null)
            return false;

        return type.IsGenericType
            && typeof(ObservableCollection<>) == type.GetGenericTypeDefinition();
    }
}