blog:
comment:
1. wait-for-idle
view 与view 之间转换的时候，为了保证有效的manipulation 和assertion，等待app处于稳定的状态再执行操作
_ = self.expectationForPredicate(
NSPredicate(format: "self.count = 1"),
evaluatedWithObject: XCUIApplication().tables,
handler: nil)
self.waitForExpectationsWithTimeout(5.0, handler: nil)
2. read accessibility info
原文：http://www.cnblogs.com/JulieandJulia/p/5519572.html