Dist::Zilla::Tester dies when run from a read-only working directory

[ppisar]

An example of Dist::Zilla::Tester dying when a test of Dist-Zilla-Plugin-Git is run from read-only location:

$ perl -I. t/tag.t 
1..8
Error in tempdir() using tmp/XXXXXXXXXX: Parent directory (tmp) does not exist at /usr/share/perl5/vendor_perl/Dist/Zilla/Tester.pm line 142.
# Looks like your test exited with 2 before it could output anything.

The cause is that Dist::Zilla::Tester defaults to ./tmp and "mkdir $tempdir_root " failure is not handled:

  around from_config => sub {
    my ($orig, $self, $arg, $tester_arg) = @_;

    confess "dist_root required for from_config" unless $arg->{dist_root};

    my $source = $arg->{dist_root};

    my $tempdir_root = exists $tester_arg->{tempdir_root}
                     ? $tester_arg->{tempdir_root}
                     : 'tmp';

    mkdir $tempdir_root if defined $tempdir_root and not -d $tempdir_root;

→   my $tempdir_obj = File::Temp->newdir(
      CLEANUP => 1,
      (defined $tempdir_root ? (DIR => $tempdir_root) : ()),
    );
    [...]

I recommend stop using ./tmp and leave selecting the temporary directory on File::Temp->newdir(). It's much smarter when finding a place for the temporary object. ./tmp is also insecure because an attacker can implant symlink of that name.