assertThrows(IllegalArgumentException.class, () -> new SmbRandomAccessFile(file, "badmode"));
    }

    @Test
    @DisplayName("open(): acquires and releases handle (no I/O)")
    void open_acquiresAndReleasesHandle() throws Exception {
        SmbRandomAccessFile raf = spy(newInstance("rw", false, true, false));
        SmbFileHandleImpl fh = mock(SmbFileHandleImpl.class);
        doReturn(fh).when(raf).ensureOpen();