From type/Test

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multi sub dies-ok(Callable $code, $reason = '')

Marks a test as passed if the given $code throws an exception.

The function accepts an optional description of the test.

sub saruman(Bool :$ents-destroy-isengard) {
    die "Killed by Wormtongue" if $ents-destroy-isengard;
}
 
dies-ok { saruman(ents-destroy-isengard => True) }, "Saruman dies";