Xcode UI tests: waitForNonExistence(...) extension function

The XCUIElement.waitForExistence(timeout:) function is great for waiting on an element to appear whilst an animation or asynchronous operation completes. However, there's equally a need at times to wait for an element to disappear and, sadly, XCUIElement does not offer such a function. Good news though! It turns out that it's not difficult at all to compose an extension function on XCUIElement which does exactly this, as follows:

extension XCUIElement {

    /**
     * Waits the specified amount of time for the element’s `exists` property to become `false`.
     *
     * - Parameter timeout: The amount of time to wait.
     * - Returns: `false` if the timeout expires without the element coming out of existence.
     */
    func waitForNonExistence(timeout: TimeInterval) -> Bool {

        let timeStart = Date().timeIntervalSince1970

        while (Date().timeIntervalSince1970 <= (timeStart + timeout)) {
            if !exists { return true }
        }
 
        return false
    }

You can find this extension function and others like it in the XCTestExtensions repo.