Got it working
here is the thing
Command="{Binding Path=DataContext.TestCommand, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"
<ItemsControl DataContext="{Binding}" ItemsSource="{Binding lm}"> Command="{Binding Path=DataContext.TestCommand, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" so the RelativeSource was the thing I've missed.
if somebody has a good explaination of this, I would be definitely happy.