public void verifyNoExceptions() {
        if (this.firstException != null)
            throw new AssertionError(this.firstException);
    }
An UncaughtExceptionHandler that can be registered with one or more threads which tracks the
first exception so the main thread can check for uncaught exceptions.
connect/runtime/src/test/java/org/apache/kafka/connect/util/TestBackgroundThreadExceptionHandler.java