build: Workaround Tap::Harness verbose misbehavior on parallel mode

The Tap::Harness module misbehaves when enabling both parallel and
verbose mode, where the verbose output is eaten by some concurrency
statistics output, and only the last test output is emitted.

We set the formatter_class explicitly to the file formatter in case we
are running in verbose and parallel modes as a workaround.

Ref: Perl-Toolchain-Gang/Test-Harness#105

build-aux/test-runner

@@ -13,6 +13,14 @@ $ENV{LC_ALL} = 'C';
 $ENV{DPKG_COLORS} = 'never';
 $ENV{PATH} = "$binroot/src:$binroot/scripts:$binroot/utils:$ENV{PATH}";
 
+my %options;
+# XXX: We need force the file formatter to workaround verbose + parallel
+# not working correctly, as the console formatter eats the test output,
+# see <https://github.com/Perl-Toolchain-Gang/Test-Harness/issues/105>.
+if ($ENV{TEST_VERBOSE} && $ENV{TEST_PARALLEL} > 1) {
+    $options{formatter_class} = 'TAP::Formatter::File';
+}
+
 my $harness = TAP::Harness->new({
     exec => sub {
         my (undef, $test) = @_;
@@ -27,6 +35,7 @@ my $harness = TAP::Harness->new({
     verbosity => $ENV{TEST_VERBOSE},
     jobs => $ENV{TEST_PARALLEL},
     failures => 1,
+    %options,
 });
 
 my $aggregate = $harness->runtests(@ARGV);