We didn't mock `os.kill` in `test_dead_process` and the pid it
kills might coincidentlly be the same with some real process.
1. Add a mocker to mock out `os.kill` in `test_dead_process`.
2. Use reset_mock to replace setting it again.
fix: #7062
1. Add `send_signal`, `kill`, `terminate` to processManager.
2. Add tests for each of them.
Co-authored-by: Peter Rowlands (변기호) <[email protected]>
karajan1001
