Suppose I have a function that caches results so it will calculate things only once. It's implemented in this way: 
sub foo ($) {
    my $arg = shift;
    state %cache;

    return $cache{$arg} if exists $cache{$arg};

    my $result = ... something costly ...;
    
    $cache{$arg} = $result;
}

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How would you write a test that checks whether the cache is actually used? Clearly you cannot access %cache to test as its lexical in the sub.

BTW, I know about Memoize. But "use Memoize" isn't an answer to the question.

In reply to How to test caching? by JavaFan

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