We should also decide how to release this once reviewed and approved. Obviously this can be merged into master but do we then release 02-03-00 from master (i.e. also rolling-up all other changes that have accumulated there) or do we cherry-pick this commit to a branch based on 02-02-00 and release 02-02-01 from that? I'm not sure that we want to release everything that's in master right now, i.e. before we finish fixing all the models that show problems in the tests. So I would tend towards releasing in a patch release.

In D96#2504, @jback wrote:

Thanks for updating the interface, Tom. I agree that it will be easier to release this as a patch release based on R02-02-00.

We don't have any Pythia-specific JSON tests at the moment, although the scripts genAllDecayExamples.sh and compareAllDecays.sh can be used to generate and compare momentum and multiplicity histograms for a range of Pythia modes, although I don't think we currently have reference Pythia ROOT files for the comparison script.

Many thanks @jback, I've successfully run the genAllDecayExamples.sh and am now also running it from a build of the master branch with Pythia8 version 309 and will then run the comparison script. Will report back what I find.

Comparisons look good I think.
You can find the plots here:
/home/epp/phsdba/Development/EvtGen/pythia8-build-problem/install/share/EvtGen/validation/gifFiles
if you want to take a quick look.