### Question:
RackErrors { public void flush() { if (buffer.length() > 0) { logger.error(buffer.toString()); buffer.setLength(0); } } RackErrors(Logger logger); void puts(String message); void write(String message); void flush();  }### Answer:
@Test public void flushOnEmpty() { rackErrors.flush(); verify(logger, never()).error(anyString()); }