end
function test_drop_file_saves_previous()
  io.write('\ntest_drop_file_saves_previous')
  App.screen.init{width=Margin_left+300, height=300}
  -- initially editing a file called foo that hasn't been saved to filesystem yet
  Lines = load_array{'abc', 'def'}
  Filename = 'foo'
  schedule_save()
  -- now drag a new file bar from the filesystem
  App.filesystem['bar'] = 'abc\ndef\nghi\n'
  local fake_dropped_file = {
    opened = false,
    getFilename = function(self)
                    return 'bar'
                  end,
    open = function(self)
             self.opened = true
           end,
    lines = function(self)
              assert(self.opened)
              return App.filesystem['bar']:gmatch('[^\n]+')
            end,
    close = function(self)
              self.opened = false
            end,
  }
  App.filedropped(fake_dropped_file)
  -- filesystem now contains a file called foo
  check_eq(App.filesystem['foo'], 'abc\ndef\n', 'F - test_drop_file_saves_previous')

  -- first make sure to save edits on any existing file
  if Next_save then
    save_to_disk(Lines, Filename)
  end
  -- clear the slate for the new file