I would compare to int because it says what I mean, and it will work in some strange cases where the regexp won't.

use Test::More 'tests' => 2;

my $x = 1 - 2**-52;

ok( $x != int $x, 'int method works' );
# this test fails
ok( $x =~ /\./, 'RegExp method works' );
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Basically, don't treat your numbers as strings if you don't have to.