SftpClient client = new SftpClient("local");
Field channelField = client.getClass().getDeclaredField("channelSftp");
channelField.setAccessible(true);
ChannelSftp mockChannel = mock(ChannelSftp.class);
when(mockChannel.ls(anyString())).thenThrow(exceptionToThrow);
channelField.set(client, mockChannel);
return client;
}