def test_lockReleasedBeforeCheck(self):
        """
        If the lock is initially held but then released before it can be
        examined to determine if the process which held it still exists, it is
        acquired and the C{clean} and C{locked} attributes are set to C{True}.
        """
        def fakeReadlink(name):
            # Pretend to be another process releasing the lock.
            lockfile.rmlink(lockf)
            # Fall back to the real implementation of readlink.
            readlinkPatch.restore()
            return lockfile.readlink(name)
        readlinkPatch = self.patch(lockfile, 'readlink', fakeReadlink)

        def fakeKill(pid, signal):
            if signal != 0:
                raise OSError(errno.EPERM, None)
            if pid == 43125:
                raise OSError(errno.ESRCH, None)
        self.patch(lockfile, 'kill', fakeKill)

        lockf = self.mktemp()
        lock = lockfile.FilesystemLock(lockf)
        lockfile.symlink(str(43125), lockf)
        self.assertTrue(lock.lock())
        self.assertTrue(lock.clean)
        self.assertTrue(lock.locked)

        If the lock is initially held but then released before it can be
        examined to determine if the process which held it still exists, it is
        acquired and the C{clean} and C{locked} attributes are set to C{True}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_lockfile.py