Covering all code paths is not necessarily possible. The range of possible value may be environment dependent and too large to test in any reasonable amount of time. Consider the following:

sub makeUserSelectedObjectDance {
   # ENVIRONMENT DEPENDENT!!!
   # any class in @INC that has a dance method will be accepted
   my ($sClass) = @_;
   return if ! ($sClass->can('dance'));

   my $oDancer = $sClass->new();
   $oDancer->dance();
   return $oSomething;
}
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or consider this routine which allows any valid combination of class and method. This kind of thing isn't all that uncommon when coding event-driven frameworks:

sub applyUserSelectedActionToUserSelectedTarget {
   # ENVIRONMENT DEPENDENT!!! - relative to codebase size and contents
   # number of valid parings of class and method can be quite large
   # in a large codebase
   my ($sClass, $sMethod) = @_;
   my $crMethod = $sClass->can($sMethod);
   return if ! $crMethod;

   my $oSomething = $sClass->new();
   $oSomething->$crMethod();
   return $oSomething;
}
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Best, beth