Lightweight waiting API for XCUITests based on NSPredicate

lightweight_waiting_API_for_XCUITests.swift

let standardTimeout:Double = 10
let shortTimeout: Double = 5

//------ Definition

func wait(for object: Any, satisfying predicateFormat: String, errorMessage: String, fails: Bool = true, timeout:Double = standardTimeout, completion: (()->())? = nil) {
    let predicate = NSPredicate(format: predicateFormat)
    let expectation = XCTNSPredicateExpectation(predicate: predicate, object: object)
    let result = XCTWaiter().wait(for: [expectation], timeout: timeout)
    if (result != .completed) {
        if (fails) {
            XCTFail(errorMessage)
        }
    } else {
        completion?()
    }
}

//------ Use

// 1. Wait for existence
let loginButton = XCUIApplication().buttons["LoginButtonIdentifier"]
wait(for: loginButton, satisfying: "exists == YES", errorMessage: "Could not find login/logout button", 
    fails: false, timeout: standardTimeout) {
    // perform action
}


// 2. Wait for change of value
let navBarLeftButton = XCUIApplication().navigationBars.buttons["LogoutButtonIdentifier"]
wait(for: navBarLeftButton, satisfying: "label == \"logout\"", errorMessage: "Could not login")