@SuppressWarnings("ResultOfMethodCallIgnored")
  private void writeSignal(final String signal) {
    try {
      final File callbackFile = new File(callbackDir, PLUGIN_LIFECYCLE_PREFIX + signal);
      if (!callbackFile.getParentFile().exists()) {
        callbackFile.getParentFile().mkdirs();
        callbackFile.getParentFile().deleteOnExit();
      }
      Files.write(
          callbackFile.toPath(),
          Collections.singletonList(
              signal + "\ntestOption=" + testOption + "\nid=" + System.identityHashCode(this)));
      callbackFile.deleteOnExit();
    } catch (final IOException ioe) {
      throw new RuntimeException(ioe);
    }
  }
This is used to signal to the acceptance test that certain tasks were completed.
acceptance-tests/test-plugins/src/main/java/org/hyperledger/besu/tests/acceptance/plugins/TestPicoCLIPlugin.java