The test contains a method for creating a file that is used for process signaling.

            Files.write(path, new byte[0], StandardOpenOption.CREATE);
-           if (!Files.exists(path)) {
-                throw new Error("Newly created file " + path
-                        + " does not exist!");
-            }
        }

An unexpected exception may be thrown if file is removed between Files.write and .Files.exists. Fix is to remove Files.exist call.