Add test for 'yes' (#992)

* Directory and test for yes script with forking.

Runs yes as child process with parent reading ten lines.
May be run on alternative yes programs for comparison.

* Added argument test to t/yes/yes.t.

* Attempted reformat of yes.t to match preferred coding style.

* remove extraneous file

Author: ludovic-tc

t/yes/yes.t

@@ -0,0 +1,61 @@
+use strict;
+use warnings;
+
+use File::Spec;
+use Test::More;
+
+$|++; # autoflush both processes (superfluous?)
+
+subtest 'test yes' => sub {
+    # set default path to yes as seen from PPT root directory
+    my $yes_path = './bin/yes';
+    # Amend path to PPT yes, if required, by setting environment
+    # variable YESPATH. This may also be used to compare with
+    # other yes implementations, e.g. at /usr/bin/yes.
+    if (defined($ENV{YESPATH})) {
+        $yes_path = $ENV{YESPATH};
+        diag "Testing yes at $ENV{YESPATH}";
+        }
+
+    ok -e $yes_path && -f $yes_path, "found 'yes' program at $yes_path"
+        or return; # fail rest of script
+
+    subtest 'fork and run yes in child process' => sub {
+        SKIP: {
+            skip "Don't run fork test on Windows", 1 if $^O eq 'MSWin32';
+            fork_yes($yes_path);
+            fork_yes($yes_path, 'iluvperl');
+            }
+        };
+    };
+
+sub fork_yes {
+    my ($yes_path, $yes_str) = @_;
+    my ($pid, $child);
+    $yes_str ||= 'y';
+    if ($pid = open($child, '-|', "$yes_path $yes_str")) {
+        # PARENT PROCESS
+        # read ten lines from child
+        my @lines;
+        for (1..10) {
+            # NOTE <> must be called in scalar context to prevent blocking.
+            my $line = <$child>;
+            push @lines, $line;
+            }
+
+        is $lines[0], "$yes_str\n", "First line is '$yes_str'.\n"; # superfluous?
+        is scalar(@lines), 10, 'Expected no. of output lines (10).';
+        my $count_of_ys = grep { /^$yes_str$/ } @lines;
+        note $count_of_ys;
+        is $count_of_ys, 10, "All 10 lines contain '$yes_str' only.\n";
+
+        close($child); # apparently superfluous
+        }
+    else {
+        die "cannot fork:$!\n" unless defined $pid;
+        # CHILD PROCESS
+        exit; # apparently superfluous
+        }
+    }
+
+done_testing();