pidof: Add test for no name and no pid found case.

src/uu/pidof/src/pidof.rs

@@ -25,6 +25,12 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     };
 
     let mut collected = collect_matched_pids(&matches);
+
+    if collected.is_empty() {
+        uucore::error::set_exit_code(1);
+        return Ok(());
+    };
+
     collected.sort_by(|a, b| b.pid.cmp(&a.pid));
 
     let output = collected

tests/by-util/test_pidof.rs

@@ -21,3 +21,15 @@ fn test_find_init() {
 fn test_find_kthreadd() {
     new_ucmd!().arg("kthreadd").succeeds();
 }
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_no_program() {
+    new_ucmd!().fails().code_is(1);
+}
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_no_pid_found() {
+    new_ucmd!().arg("NO_THIS_PROGRAM").fails().code_is(1);
+}