Assert log events in logback

logbackAsserts.groovy

private final static Set<ILoggingEvent> loggingEvents = [] as Set
 
private void reset() {
  loggingEvents.clear()
  initializeMockLogAppender();
}

public void assertOneErrorLogEvent(String expectedMessage) {
    assert loggingEvents.size() == 1
    assert loggingEvents.first().getThrowableProxy().message == expectedMessage
}

private void initializeMockLogAppender() {
    final appender = new MockAppender(Level.ERROR,
            [SomeClass.class.name, SomeOtherClass.class.name])

    final rootLogger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
    appender.setContext(rootLogger.getLoggerContext())
    appender.start()

    rootLogger.addAppender(appender);
}
 
private static class MockAppender extends AppenderBase<ILoggingEvent> {
    private final Level levelFilter;
    private final List<String> loggerNameFilter;

    MockAppender(Level levelFilter, List<String> loggerNameFilter) {
        this.levelFilter = levelFilter
        this.loggerNameFilter = loggerNameFilter
    }

    @Override
    protected void append(final ILoggingEvent loggingEvent) {
        if (loggingEvent.level == levelFilter && loggerNameFilter.contains(loggingEvent.getLoggerName())) {
            loggingEvents.add(loggingEvent);
        }
    }
}