perl.p6

unit module Test::Output;

my class IO::Bag {
    has @.err-contents;
    has @.out-contents;
    has @.all-contents;

    method err { @.err-contents.join: '' }
    method out { @.out-contents.join: '' }
    method all { @.all-contents.join: '' }
}

my class IO::Capture::Single is IO::Handle {
    has Bool    $.is-err =  False   ;
    has IO::Bag $.bag    is required;

    method print-nl { self.print($.nl-out); }
    method print (*@what) {
                    $.bag.all-contents.push: @what.join: '';
        $!is-err ?? $.bag.err-contents.push: @what.join: ''
                 !! $.bag.out-contents.push: @what.join: '';

        True;
    }
}

sub output-is (&code, Regex $expected, $test-name = 'output matches' )
    is export
{
    my $bag = IO::Bag.new;
    my $out = IO::Capture::Single.new: :$bag        ;
    my $err = IO::Capture::Single.new: :$bag :is-err;
    {
        my $*OUT = $out;
        my $*ERR = $err;
        &code();
    }
    say "STDOUT is {$bag.out}";
    say "STDERR is {$bag.err}";
    say "MERGED is {$bag.all}";

    return :out(~$bag.out), :err(~$bag.err), :all($bag.all);
}