'no_plan' is good when you're willy-nilly writing tests and don't want to keep jumping to the top of your file to update the number of tests. (Alternative frameworks like Test::Class actually help keep count for you and it plays nicely with Test::More and friends).

If you have a knowable number of test cases, you can always count the number and pass that to the plan (either on the "use" line or with the "plan" function. For example:

use Test::More;

open my($fh), "<datafile";
my $count = do { my $i; $i++ while <$fh>; $i };
seek ( $fh, 0, 0 );

plan tests => $count;

load_database("datafile"); # or whatever

while (<$fh>) {
  ok( in_database( $_ ) );
}
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