I wonder if expressing this option in the positive would also satisfy your use case. In other words, the ability to specify one or more namespaces that should be tested, with the default being to test all if the option is empty. I think this might be more generally useful, because then you'd be able to easily run tests for a namespace like Uize.Data, for example. Expressed in the negative as namespaces to ignore, it's somewhat harder to do that. What namespaces are you wanting to have tested in your use case?