public String doLayout(ILoggingEvent event) {
        if (!isStarted()) {
            return CoreConstants.EMPTY_STRING;
        }
        return writeLoopOnConverters(event);
    }
@Test
    public void prefixConverterSmoke() {
        String pattern = "%prefix(%logger) %message";
        pl.setPattern(pattern);
        pl.start();
        String val = pl.doLayout(makeLoggingEvent("hello", null));
        assertEquals("logger=" + logger.getName() + " hello", val);
    }