Test that negative numbers are not accepted

ci/test-03-forbidden.pl

@@ -1,6 +1,6 @@
 #!/usr/bin/perl -w
 
-use Test::Command tests => 24;
+use Test::Command tests => 36;
 
 # fping -i 0
 my $cmd1 = Test::Command->new(cmd => "fping -i 0 -T10 -g 127.0.0.1/29");
@@ -56,3 +56,10 @@ $cmd10->exit_is_num(1);
 $cmd10->stdout_is_eq("");
 $cmd10->stderr_is_eq("fping: backoff factor 5.1 not valid, must be between 1.0 and 5.0\n");
 
+# non-negative only
+for my $arg (qw(i p Q t)) {
+    my $cmd = Test::Command->new(cmd => "fping -$arg -1");
+    $cmd->exit_is_num(1);
+    $cmd->stdout_is_eq("");
+    $cmd->stderr_like(qr{Usage:});
+}