docs: def browse(self):
          ''' Browse the history of a single file
          adds one commit that doesn't contain changes in test_file_1.
          there are four commits in summary, so the check for buffer line
          count compares with 3.
          at the end, a fifth commit must be present due to resetting the
          file contents.
          '''
          check = self._check
          marker_text = Random.string()
          self.vim.buffer.set_content([marker_text])
          self._save()
          self._write_file(1)
          self._save()
          self._write_file2(1)
          self._save()
          self._write_file(2)
          self._write_file2(1)
          self._save()
          self.vim.cmd('ProHistoryFileBrowse {}'.format('test_file_1'))
          check(0, '*')
          self.vim.vim.feedkeys('j')
          self.vim.vim.feedkeys('j')
          later(lambda: self.vim.buffer.content.length.should.equal(3))
          self.vim.vim.feedkeys('s')
          self._await_commit(0)
          self.vim.buffer.content.should.equal(List(marker_text))