subtest with implicit done_testing

---

examples/test-more/t/subtest.t

use strict;
use warnings;

use MySimpleCalc qw(sum);

use Test::More;

subtest positives => sub {
    is sum(1, 1), 2,  '1+1';
    is sum(2, 2), 4,  '2+2';
};

subtest negatives => sub {
    is sum(-1, -1), -2, '-1, -1';
    is sum(-1, -1, -1), -3, '-1, -1, -1';
};

done_testing;

    #   Failed test '-1, -1, -1'
    #   at t/subtest.t line 15.
    #          got: '-2'
    #     expected: '-3'
    # Looks like you failed 1 test of 2.

#   Failed test 'negatives'
#   at t/subtest.t line 16.
# Looks like you failed 1 test of 2.
t/subtest.t .. 
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/2 subtests 

Test Summary Report
-------------------
t/subtest.t (Wstat: 256 Tests: 2 Failed: 1)
  Failed test:  2
  Non-zero exit status: 1
Files=1, Tests=2,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.13 cusr  0.00 csys =  0.15 CPU)
Result: FAIL

Implicit call to done_testing inside. skip-able, etc.