ip_isr has some code that is not tested, including AssembleCcdTask and likely parts of IsrTask.
Add tests for ip_isr/isrTask
AssembleCcdTask failure with Python 2
See e.g. DM-8355 for a failure which ought to be caught by the tests added here.
Closing as duplicate of DM-15683.
Marking invalid, as DM-15683 is subsuming this work (and that will eventually be marked "Done").