App.screen.init{width=300, height=300}
  Editor_state = edit.initialize_test_state()
  Editor_state.filename = 'foo'

  App.screen.init{width=Editor_state.left+300, height=300}
  Editor_state = edit.initialize_test_state()
  App.filesystem['foo'] = 'abc\ndef\nghi\n'
  local fake_dropped_file = {
    opened = false,
    getFilename = function(self)
                    return 'foo'
                  end,
    open = function(self)
             self.opened = true
           end,
    lines = function(self)
              assert(self.opened)
              return App.filesystem['foo']:gmatch('[^\n]+')
            end,
    close = function(self)
              self.opened = false
            end,
  }
  App.filedropped(fake_dropped_file)

  edit.draw(Editor_state)
end
function test_drop_file_saves_previous()
  App.screen.init{width=Editor_state.left+300, height=300}
  -- initially editing a file called foo that hasn't been saved to filesystem yet
  Editor_state.lines = load_array{'abc', 'def'}
  Editor_state.filename = 'foo'
  schedule_save(Editor_state)
  -- 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

end