use Test::More tests => 2;

ok(1, "First test");

$pid = open( CHILD, "|-" );
$SIG{PIPE} = 'IGNORE';

if ($pid) {    # parent
    print CHILD "test\n";
    close CHILD;
    exit 0;
}

# child process

ok(1, "Second test");
[download]

The output is as follows:

1..2
ok 1 - First test
ok 2 - Second test
# Looks like you planned 2 tests but only ran 1.
[download]

Notice that the test did execute, and it did print to STDOUT, but Test::More didn't see it, hence it wasn't counted.

Here is the same test without using Test::More:

print "1..2\n";
print "ok 1 - First test\n";

$pid = open( CHILD, "|-" );
$SIG{PIPE} = 'IGNORE';

if ($pid) {    # parent
    print CHILD "test\n";
    close(CHILD);
    exit 0;
}
print "ok 2 - Second test\n";
[download]

Obviously this second test will just output the simple printed data to STDOUT, but to highlight that it works properly, you can run it through Test::Harness to see that it works OK, and that the Test::More version fails:

# perl -MTest::Harness -e 'runtests("test_plain_fork.t", "test_more_fo
+rk.t")'

test_plain_fork....ok
test_more_fork.....ok 2/2# Looks like you planned 2 tests but only ran
+ 1.
test_more_fork.....dubious
        Test returned status 1 (wstat 256, 0x100)
        after all the subtests completed successfully
Failed Test      Stat Wstat Total Fail  Failed  List of Failed
----------------------------------------------------------------------
+---------
test_more_fork.t    1   256     2    0   0.00%  ??
Failed 1/2 test scripts, 50.00% okay. 0/4 subtests failed, 100.00% oka
+y.
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I have a feeling this is all because of Test::Builder, which has this comment in the docs:

It's ok for your test to change where STDOUT and STDERR point to, Test::Builder's default output settings will not be affected.

If that is the problem, is there any way around it? If it isn't the problem, what am I doing wrong?