An alternative to this:

my $strings = $mock->files;
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Would be this:

my @strings = @{ $mock->files };
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Or if you've got a very recent version of Perl:

my @strings = $mock->files->@*;
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Moose also has an optional feature where it can detect if an accessor is called in a list context and return a list instead of a reference, but Moo didn't implement that because it can get confusing to work with.