how do I test that a function returns nothing when called in void context?

Two thoughts:

1. Why would it matter?

   If a function returned a value in a void context, it is just discarded.

   Not returning anything in a void context is not the point, it is not calculating the return values if they are never going to be used that makes a difference.

2. Testing something that is obvious by inspection is a waste of time.

   If the first line of the sub is return unless defined wantarray;, the sub will not return anything when called in a void context. There is no need to test that.

Thanks for your reply.

I think you answer has pointed me in the right direction: I am trying to test for the wrong thing. I should be testing (perhaps via a mock object or similar), that my function does not do anything expensive (e.g., call a database function) to return a result when called in void context. I was erroneously focusing on the return result, rather than the operations of my function. Testing the return value (or lack thereof) would not prove if my function was performing a pointless operation.

Thanks!

As a general thing though, one may often call a method in a void context and expect something expensive to happen (connecting to a remote database for example), especially if you use exception handling to manage errors rather than passing error states back.

True laziness is hard work

I should be testing (perhaps via a mock object or similar), that my function does not do anything expensive (e.g., call a database function) to return a result when called in void context.

Such as playing nethack? :)

Parens don't create lists*.

return wantarray ? ('value') : 'value';
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return wantarray ? 'value' : 'value';
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return 'value';
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* — Except on the LHS of an assignment (indirectly) and inside of a list literal.

sub Foo::bar { return 42; }
say '1: ', Foo::bar;

{
    no warnings 'redefine';
    local *Foo::bar = sub { die };

    eval { say '2: ', Foo::bar; };
}

say '3: ', Foo::bar;

__END__

1: 42
3: 42
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