How to select a picker view item in an iOS UI test in Xcode?

Swift 4 version of @Joao_dche's answer

app.pickerWheels.element(boundBy: 0).adjust(toPickerWheelValue: "March")
app.pickerWheels.element(boundBy: 1).adjust(toPickerWheelValue: "13")
app.pickerWheels.element(boundBy: 2).adjust(toPickerWheelValue: "1990")

If there are multiple wheels, an easy way to select items it is like this:

precondition: it's a date picker (UIDatePicker), swift language

    app.pickerWheels.elementBoundByIndex(0).adjustToPickerWheelValue("March")
    app.pickerWheels.elementBoundByIndex(1).adjustToPickerWheelValue("13")
    app.pickerWheels.elementBoundByIndex(2).adjustToPickerWheelValue("1990")

where: index "0" is month, "1" is day, "2" is year

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.

Objective-C Version of @Joao_dche's Answer

Using UIDatePicker with XCTest for UI Testing:

    XCUIElementQuery *datePickersQuery = app.datePickers;
    [datePickersQuery.pickerWheels.allElementsBoundByIndex[0] adjustToPickerWheelValue:@"May"];
    [datePickersQuery.pickerWheels.allElementsBoundByIndex[1] adjustToPickerWheelValue:@"13"];
    [datePickersQuery.pickerWheels.allElementsBoundByIndex[2] adjustToPickerWheelValue:@"2017"];

    XCUIElement *doneButton = app.buttons[@"Done"];
    [doneButton.firstMatch tap];