Test that -x, -X, -k require numeric argument

ci/test-12-option-type.pl

@@ -1,10 +1,22 @@
 #!/usr/bin/perl -w
 
-use Test::Command tests => 33;
+use Test::Command tests => 42;
+use Test::More;
 
-for my $arg (qw(b B c C H i O p Q r t)) {
+for my $arg (qw(b B c C H i O p Q r t x X)) {
     my $cmd = Test::Command->new(cmd => "fping -$arg xxx");
     $cmd->exit_is_num(1);
     $cmd->stdout_is_eq("");
     $cmd->stderr_like(qr{Usage:});
 }
+
+# fping -k, only supported on Linux, requires a number
+SKIP: {
+    if($^O ne 'linux') {
+        skip '-k option is only supported on Linux', 3;
+    }
+    my $cmd = Test::Command->new(cmd => 'fping -k xxx 127.0.0.1');
+    $cmd->exit_is_num(1);
+    $cmd->stdout_is_eq("");
+    $cmd->stderr_like(qr{Usage:});
+}