Flesh out tests for run/shell a bit.

We had not tests that checked the return type of run and shell at all.
This codifies that they return Proc and along the way covers the final
design that RT #117039 was complaining about.

S29-os/system.t

@@ -4,19 +4,34 @@ use Test;
 # L<S29/"OS"/"=item run">
 # system is renamed to run, so link there. 
 
-plan 8;
+plan 18;
 
 my $res;
 
-$res = run($*EXECUTABLE,'-e1');
+$res = run($*EXECUTABLE,'-e', '');
 ok($res,"run() to an existing program does not die (and returns something true)");
+isa-ok($res, Proc, 'run() returns a Proc');
+is($res.exitcode, 0, 'run() exit code when successful is zero');
 
+$res = shell("$*EXECUTABLE -e \"\"");
+ok($res, "shell() to an existing program does not die (and returns something true)");
+isa-ok($res, Proc, 'shell() returns a Proc');
+is($res.exitcode, 0, 'shell() exit code when successful is zero');
+
+# RT #117039
 $res = run("program_that_does_not_exist_ignore_this_error_please.exe");
 ok(!$res, "run() to a nonexisting program does not die (and returns something false)");
+isa-ok($res, Proc, 'run() returns a Proc even when not successful');
+ok($res.exitcode != 0, 'run() exit code is not zero on failure');
 
 $res = run("program_that_does_not_exist_ignore_errors_please.exe","a","b");
 ok(!$res, "run() to a nonexisting program with an argument list does not die (and returns something false)");
 
+$res = shell("program_that_does_not_exist_ignore_this_error_please.exe");
+ok(!$res, "shell() to a nonexisting program does not die (and returns something false)");
+isa-ok($res, Proc, 'shell() returns a Proc even when not successful');
+ok($res.exitcode != 0, 'shell() exit code is not zero on failure');
+
 # RT #104794
 {
     use lib 't/spec/packages';