Add regression test for Process::parent update

test_bin/main.rs

@@ -1,5 +1,25 @@
 // Does nothing and just exits after waiting for 30 seconds.
 
+use std::process::{Child, Command};
+
+fn maybe_start_child(last: String, args: &[String]) -> Option<Child> {
+    if last == "1" {
+        let mut cmd = Command::new(&args[0]);
+        for arg in &args[1..] {
+            cmd.arg(arg);
+        }
+        Some(cmd.spawn().expect("failed to run command"))
+    } else {
+        None
+    }
+}
+
 fn main() {
-    std::thread::sleep(std::time::Duration::from_secs(30));
+    let mut args: Vec<String> = std::env::args().collect();
+    let child = args.pop().and_then(|last| maybe_start_child(last, &args));
+    if child.is_some() {
+        std::thread::sleep(std::time::Duration::from_secs(3));
+    } else {
+        std::thread::sleep(std::time::Duration::from_secs(30));
+    }
 }

tests/process.rs

@@ -801,3 +801,50 @@ fn test_process_run_time() {
         run_time
     );
 }
+
+// Test that if the parent of a process is removed, then the child PID will be
+// updated as well.
+#[test]
+fn test_parent_change() {
+    if !sysinfo::IS_SUPPORTED_SYSTEM || cfg!(feature = "apple-sandbox") {
+        return;
+    }
+
+    build_test_binary();
+    let mut p = std::process::Command::new("./target/test_binary")
+        .arg("1")
+        .spawn()
+        .unwrap();
+
+    std::thread::sleep(std::time::Duration::from_secs(1));
+
+    let pid = Pid::from_u32(p.id() as _);
+    let mut s = System::new();
+    s.refresh_processes();
+
+    assert_eq!(
+        s.process(pid).expect("process was not created").parent(),
+        sysinfo::get_current_pid().ok(),
+    );
+
+    let child_pid = s
+        .processes()
+        .iter()
+        .find(|(_, proc_)| proc_.parent() == Some(pid))
+        .map(|(pid, _)| *pid)
+        .expect("failed to get child process");
+
+    // Waiting for the parent process to stop.
+    p.wait().expect("wait failed");
+
+    s.refresh_processes();
+    // Parent should not be around anymore.
+    assert!(s.process(pid).is_none());
+
+    let child = s.process(child_pid).expect("child is dead");
+    // Child should have a different parent now.
+    assert_eq!(child.parent(), None);
+
+    // We kill the child to clean up.
+    child.kill();
+}