# Pastebin 02Zcq1m7
      {
          class TestOnDemandSupply does Tappable {
              method tap(&emit, &, &, &tap) {
                  my $t = $*SCHEDULER.cue({.&emit for ^4});
                  tap($t);
                  $t
              }
              method sane\      (--> True)  {}
              method serial\    (--> False) {}
              method live\      (--> False) {}
          }
          subtest {
              react {
                  whenever Promise.in(10) {
                      flunk "zip timed out";
                      done;
                  }
                  whenever Supply.zip: Supply.from-list(^2), Supply.new(TestOnDemandSupply.new) -> $l {
                      .say;
                      if $l eqv ((0, 0) | (1, 1)) {
                          pass "zip is ok"
                      } else {
                          flunk "invalid value: $l"
                      }
                      LAST { done }
                  }
              }
          }
      }