skip '$ENV{WANT_HONKING_BIG_TEST} is not set', 1
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As for a standard name (it's arbitrary, so why not agree on a standard name?) for said environment variable, this has been discussed a number of times on perl-qa mailing list here and here and here and in a few other places as well (discussion triggered by Skip tests if/unless $ENV{FOO} is set using Test::More). Alas, I don't think a consensus was ever reached. :-( Maybe if someone suggested your WANT_HONKING_BIG_TEST we might have got a consensus. :-)