@Test
public void testWarn() throws Exception {

    Logger logger = Mockito.mock(Logger.class);
    when(logger.isWarnEnabled()).thenReturn(true);
    LogHelper.warn(logger, "warn");
    verify(logger).warn("warn");
    Throwable t = new RuntimeException();
    LogHelper.warn(logger, t);
    verify(logger).warn(t);
    LogHelper.warn(logger, "warn", t);
    verify(logger).warn("warn", t);
}