You can have as much prep code as you want between calls to ok (and the like). There's nothing special about ok. It's just a function that checks if the value you passed to it is true or not, and prints out something appropriate in response.

my ($x, $y) = (1, 2);
is($x, 2, 'x');
is($y, 3, 'y');
$x += 4;
is($x, 6, '+=');
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(I used is instead of ok since there's rarely any reason to use ok.)