code: function (root, componentType) {
      var all = ReactTestUtils.scryRenderedComponentsWithType(root, componentType);
      if (all.length !== 1) {
        throw new Error('Did not find exactly one match (found: ' + all.length + ') ' + 'for componentType:' + componentType);
      }
      return all[0];
    }
docs: Same as `scryRenderedComponentsWithType` but expects there to be one result
  and returns that one result, or throws exception if there is any other
  number of matches besides one.
  @return {!ReactComponent} The one match.