'Edit the yaml file appending an extra field to the first item, then
apply changes.'

def test_single_edit_add_field(self, mock_write):

    self.run_mocked_command({'replacements': {u'id:    1': u'id:    1\nfoo:    bar'}}, ['a'])
    self.assertEqual(self.lib.items(u'id:1')[0].foo, 'bar')
    self.assertCounts(mock_write, write_call_count=1, title_starts_with=u't\xeftle')
