Of course they tested Doom :-D
They might also run Linux kernel 3.7, that supported i386. Gray386linux is still maintained, and runs a patched 3.7 kernel.
Doom (DOS extender games) is an easier protected mode application as it does not use complex page tables. Linux is much more complex.
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haha, this was my first thought when I read the headline, because this "classic test" always comes up here :-))