wait for condition to be true

WaitUntil.swift

// https://gist.github.com/JARinteractive/7fb33b6b0043f365ddfd
import Foundation
import XCTest

@discardableResult
public func AssertEventuallyTrue(file: StaticString = #file, line: UInt = #line, _ checkSuccess: @autoclosure () -> Bool) -> Bool {
    return AssertEventuallyTrue(10.0, file: file, line: line, checkSuccess)
}

@discardableResult
public func AssertEventuallyTrue(_ timeout: Double, file: StaticString = #file, line: UInt = #line, _ checkSuccess: @autoclosure () -> Bool) -> Bool {
    let startDate = NSDate()
    var success = false
    while !success && abs(startDate.timeIntervalSinceNow) < timeout {
        RunLoop.current.run(until: Date(timeIntervalSinceNow: 0.01))
        success = checkSuccess()
    }
    if !success { XCTFail("Timeout occurred while waiting for condition (waitUntil)", file: file, line: line) }
    return success
}

Add @discardableResult if you want those missing assignment warnings to go away