If you don't need a recursive search, davido's idea to use glob is preferable. If you do, however, File::Find is a fine solution. Your sub can be cleaned up a bit, though:

sub get_files {
    my $directory = shift;    
    
    my @files;
    
    find(sub { 
        return unless /\.t$/;

        my $n = $File::Find::name;
        $n =~ tr{\\}{/};
        push @files, $n;
    }, $directory);

    return @files;
}
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