One possible solution to this would be to create test scripts (e.g. using Test::More) for the module in question:

package foo;
use warnings;
use strict;
sub monk {
  return 42;
}
sub go {
  return mink(123);
}
1;
__END__
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use strict;
use warnings;

use Test::More tests => 3;
use lib qw (.);

BEGIN {
  use_ok('foo');
}

# ------ monk ------
cmp_ok(foo::monk(), q{==}, 42, q{Expect monk to return 42});

# ------ go ------
cmp_ok(foo::go(), q{==}, 42, q{Expect go to return 42});
__END__
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Running the test yields:

$ prove foo.t
foo....ok 1/3Undefined subroutine &foo::mink called at foo.pm line 8.
# Looks like you planned 3 tests but only ran 2.
# Looks like your test died just after 2.
foo....dubious
        Test returned status 255 (wstat 65280, 0xff00)
DIED. FAILED test 3
        Failed 1/3 tests, 66.67% okay
Failed Test Stat Wstat Total Fail  List of Failed
----------------------------------------------------------------------
+---------
foo.t        255 65280     3    2  3
Failed 1/1 test scripts. 1/3 subtests failed.
Files=1, Tests=3,  1 wallclock secs ( 0.04 cusr +  0.00 csys =  0.04 C
+PU)
Failed 1/1 test programs. 1/3 subtests failed.
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