assertEquals("tree-fail", ex.getMessage());
        verify(handle, times(1)).ensureTreeConnected();
    }

    @Test
    @DisplayName("ensureOpen delegates and returns the file handle")
    void ensureOpen_delegatesAndReturns() throws Exception {
        // Arrange
        SmbPipeOutputStream out = newStream();
        when(handle.ensureOpen()).thenReturn(fileHandle);

        // Act