Minilla doesn't install modules in cpanfile's test phase section, when executing `minil test`

[akarelas]

I tried executing minil test on a fresh Perl-with-Minilla in my RxPerl module source directory, and got this error message:

t/finalize.t ....... ok   
t/marble.t ......... ok    
t/promises.t ....... Can't locate Promise/ES6.pm in @INC (you may need to install the Promise::ES6 module) (@INC entries checked: /home/appuser/work/RxPerl/.build/FYLCQsfI/blib/arch /home/appuser/work/RxPerl/.build/FYLCQsfI/blib/lib /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/site_perl/5.40.0/x86_64-linux /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/site_perl/5.40.0 /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/5.40.0/x86_64-linux /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/5.40.0) at /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/5.40.0/Module/Load.pm line 78.
Can't locate Promise/ES6 in @INC (@INC entries checked: /home/appuser/work/RxPerl/.build/FYLCQsfI/blib/arch /home/appuser/work/RxPerl/.build/FYLCQsfI/blib/lib /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/site_perl/5.40.0/x86_64-linux /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/site_perl/5.40.0 /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/5.40.0/x86_64-linux /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/5.40.0) at /home/appuser/.plenv/versions/5.40.0-minilla/lib/perl5/5.40.0/Module/Load.pm line 78.
t/promises.t ....... Dubious, test returned 2 (wstat 512, 0x200)

However, RxPerl's cpanfile clearly states Promise::ES6 in the test phase:

requires 'perl', '5.010';

requires 'Hash::Ordered', '0.006';
requires 'Sub::Util', '1.41';
requires 'parent';

on 'test' => sub {
    requires 'Test2::V0';
    requires 'Promise::ES6';
};

(from https://gitlab.com/karjala/rxperl/-/blob/master/cpanfile?ref_type=heads)

[akarelas]

I was wrong - it had tried to install Promise::ES6, but failed for some reason.