### Question:
AbstractLoggerFactory implements LoggerFactory { @Override public Stream<LoggerEventListener> listeners() { return listeners.stream(); } AbstractLoggerFactory(); @Override Logger create(Class<?> binding); @Override Logger create(String binding); @Override synchronized void setFormatter(LoggerFormatter formatter); @Override synchronized LoggerFormatter getFormatter(); abstract Logger make(String binding, LoggerFormatter formatter); @Override void addListener(LoggerEventListener listener); @Override void removeListener(LoggerEventListener listener); @Override Stream<LoggerEventListener> listeners(); @Override Stream<Entry<String, Logger>> loggers(); @Override void setLevel(String path, Level level); @Override void setLevel(Class<?> binding, Level level);  }### Answer:
@Test void listeners() { assertEquals(0, instance.listeners().count()); instance.addListener(loggerEventListener); assertEquals(loggerEventListener, instance.listeners().findFirst().orElseThrow(NoSuchElementException::new)); }