### Question:
UsbFileOutputStream extends OutputStream { @Override public void flush() throws IOException { file.flush(); } UsbFileOutputStream(@NonNull UsbFile file); @Override void write(int oneByte); @Override void close(); @Override void flush(); @Override void write(byte[] buffer); @Override void write(byte[] buffer, int offset, int count);  }### Answer:
@Test public void flush() throws Exception { new UsbFileOutputStream(file).flush(); verify(file).flush(); }