check_licenses [ 'woo' ], [ ], 'nonexistent';
check_licenses [ 'perl' ], [ qw/Artistic GPL-2/ ], 'perl';
check_licenses [ qw/perl gpl2/ ], [ qw/Artistic GPL-2/ ], 'perl + gpl2';
check_licenses [ 'woo' ], [ ], 'nonexistent';
check_licenses [ 'perl' ], [ qw/Artistic GPL-2/ ], 'perl';
check_licenses [ qw/perl gpl2/ ], [ qw/Artistic GPL-2/ ], 'perl + gpl2';