It's a bug that has been resolved. Here's my workaround: 
package Parent;
use Moose;
use Test::Most tests => 1, '-Test::Deep';

sub BUILD {
    my ( $self, $args ) = @_;
    if ( $args->{'tests'} ) {
        plan tests => $args->{'tests'};
    }
}

package Child;
use Moose;
use Test::Most '-Test::Deep';
extends qw(Parent);

sub run {
    my ($self) = @_;
    ok( 1, 'simple test' );
}

__PACKAGE__->new->run;

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In reply to Re: Moose: Exporting non-moose subs to child by Khen1950fx
in thread Moose: Exporting non-moose subs to child by elTriberium

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