test(io): cover real-file input to scalar-reference output (#1216)

src/test/resources/unit/filehandle_input_real_file_scalar_output.t

@@ -0,0 +1,25 @@
+use strict;
+use warnings;
+use File::Temp qw(tempfile);
+use Test::More;
+
+my ($writer, $path) = tempfile();
+print {$writer} "[% group %]\n" or die "write template: $!";
+close $writer or die "close template: $!";
+END { unlink $path if defined $path && -e $path }
+
+open my $input, '<', $path or die "open template: $!";
+my $output;
+open my $output_fh, '>', \$output or die "open scalar output: $!";
+
+while (defined(my $line = <$input>)) {
+    $line =~ s/\[% group %\]/hoge foo bar/;
+    print {$output_fh} $line or die "write scalar output: $!";
+}
+
+close $input or die "close template input: $!";
+close $output_fh or die "close scalar output: $!";
+is($output, "hoge foo bar\n",
+    'filehandle input from a real file writes to scalar-reference output');
+
+done_testing;