As noted in the question’s update, Xcode 7 Beta 6 added support for interacting with pickers. The newly added method -adjustToPickerWheelValue:
should be used to select items on a UIPickerView
.
let app = XCUIApplication()
app.launch()
app.pickerWheels.element.adjustToPickerWheelValue("Yellow")
Here’s a GitHub repo with a working example. And some more information in a blog post I wrote.