What's happening here is that your implementation (.m) for UIHelper can't be found by the UnitTest. You need to make sure your UIHelper.m is part of your app or your unit test target. See how the UIHelper.m is indicated as having target membership by the text box in the ride pane:
And, the unit test target is able to find this implementation b/c this target depends on the app target. See in the middle pane where the app is listed as a target dependency: