--- a/testing/mozbase/mozprocess/mozprocess/processhandler.py
+++ b/testing/mozbase/mozprocess/mozprocess/processhandler.py
@@ -918,17 +918,17 @@ falling back to not using job objects fo
 
         In case of application restarts the process can spawn itself into a new process group.
         From now on the process can no longer be tracked by mozprocess anymore and has to be
         marked as detached. If the consumer of mozprocess still knows the new process id it could
         check for the detached state.
 
         new_pid is the new process id of the child process.
         """
-        if not self.proc:
+        if not hasattr(self, "proc"):
             return
 
         if isPosix:
             new_pgid = self._getpgid(new_pid)
 
             if new_pgid and new_pgid != self.proc.pgid:
                 self.proc.detached_pid = new_pid
                 print('Child process with id "%s" has been marked as detached because it is no '

--- a/testing/mozbase/mozprocess/tests/manifest.ini
+++ b/testing/mozbase/mozprocess/tests/manifest.ini
@@ -1,10 +1,12 @@
 [DEFAULT]
 subsuite = mozbase, os == "linux"
 
+[test_detached.py]
+skip-if = os == "win"
 [test_kill.py]
 [test_misc.py]
-[test_poll.py]
-[test_wait.py]
 [test_output.py]
 [test_params.py]
+[test_poll.py]
 [test_process_reader.py]
+[test_wait.py]

new file mode 100644
--- /dev/null
+++ b/testing/mozbase/mozprocess/tests/test_detached.py
@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+
+from __future__ import absolute_import
+
+import os
+
+import mozunit
+
+from mozprocess import processhandler
+
+import proctest
+
+
+here = os.path.dirname(os.path.abspath(__file__))
+
+
+class ProcTestDetached(proctest.ProcTest):
+    """ Class to test process detached """
+
+    def test_check_for_detached_while_running_with_current_pid(self):
+        """Process is started, and poll() is called"""
+
+        p = processhandler.ProcessHandler([self.python, self.proclaunch,
+                                           "process_normal_finish.ini"],
+                                          cwd=here)
+        p.run()
+
+        orig_pid = p.pid
+        p.check_for_detached(p.pid)
+
+        self.assertEqual(p.pid, orig_pid)
+        self.assertIsNone(p.proc.detached_pid)
+
+        self.determine_status(p, True)
+        p.kill()
+
+    def test_check_for_detached_after_kill(self):
+        """Process is killed, and poll() is called"""
+
+        p = processhandler.ProcessHandler([self.python, self.proclaunch,
+                                           "process_normal_finish.ini"],
+                                          cwd=here)
+        p.run()
+        p.kill()
+
+        orig_pid = p.pid
+        p.check_for_detached(p.pid)
+
+        self.assertEqual(p.pid, orig_pid)
+        self.assertIsNone(p.proc.detached_pid)
+
+        self.determine_status(p)
+
+
+if __name__ == '__main__':
+    mozunit.main()