kill: add tests to check multiple output

tests/by-util/test_kill.rs

@@ -92,6 +92,28 @@ fn test_kill_list_one_signal_from_name() {
         .stdout_matches(&Regex::new("\\b9\\b").unwrap());
 }
 
+#[test]
+fn test_kill_list_two_signal_from_name() {
+    new_ucmd!()
+        .arg("-l")
+        .arg("INT")
+        .arg("KILL")
+        .succeeds()
+        .stdout_matches(&Regex::new("\\d\n\\d").unwrap());
+}
+
+#[test]
+fn test_kill_list_three_signal_first_unknown() {
+    new_ucmd!()
+        .arg("-l")
+        .arg("IAMNOTASIGNAL") // spell-checker:disable-line
+        .arg("INT")
+        .arg("KILL")
+        .fails()
+        .stderr_contains("unknown signal")
+        .stdout_matches(&Regex::new("\\d\n\\d").unwrap());
+}
+
 #[test]
 fn test_kill_set_bad_signal_name() {
     // spell-checker:disable-line