Tests
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OK different CLASS and KEY indictators
CLASS & KEY ind/attrib clash
OK single isa => 'Object'
OK ArrayRef obj
OK HashRef obj

general class of Moose attrib mis-matches, e.g. isa => 'Int', but data contains
non-int, undef, arrayref, ...
  also isa => "This", but descr class => "That"

descriptor with:
no class
got class, no attribs
sub-attr a non-ARRAY, non-HASH ref (func ref?, scalar ref?)

key col out of limits
(some of the other _check... tests?)

call atm with 1-D list but descr with sub-objects

descr contains "key => ..." but the sub-obj isn't a HashRef

object has required attrs which arent in data or descr