The visualisation is important because it provides an integration test with eyeball verification whilst the CML checks for other unwanted changes in the metadata, like central_latitude, which would produce numerical, but not visual, changes.

We could dump one of the grib edition tests but it's better with both, in case the GRIB API were to introduce a bug in the def files (which would only affect a single edition).

We could lose one of the visual tests but it makes me nervous (and I'm quite loose on testing!).

I'll do whatever it takes to get this in ASAP but I'd feel much safer with these tests in place.