XCUITesting: Writing UI Tests, Tests with Swift

Creating UI tests with XCTest is an extension of the same programming model as creating unit tests. The differences in workflow and implementation are focused around using UI recording and the XCTest UI testing APIs, described in User Interface Testing.


The difference in Swift w.r.to Objective C is that Swift has access control model. And that prevents the external entity from accessing anything declared as internal in an app or framework.

1) When you set the Enable Testability build setting to Yes, which is true by default for test builds in new projects, Xcode includes the -enable-testing flag during compilation. This makes the Swift entities declared in the compiled module eligible for a higher level of access.

2) When you add the @testable attribute to an import statement for a module compiled with testing enabled, you activate the elevated access for that module in that scope. Classes and class members marked as internal or public behave as if they were marked open. Other entities marked as internal act as if they were declared public.


Below is how to do it. With this solution in place, your Swift app code’s internal functions are fully accessible to your test classes and methods. The access granted for @testable imports ensures that other, non-testing clients do not violate Swift’s access control rules even when compiling for testing. Further, because your release build does not enable testability, regular consumers of your module (for example if you distribute a framework) can’t gain access to internal entities this way.


import XCTest

// Importing AppKit because of NSApplication
import AppKit

// Importing MySwiftApp because of AppDelegate
@testable import MySwiftApp

class MySwiftAppTests: XCTestCase {
    func testExample() {
        let appDelegate = NSApplication.sharedApplication().delegate as! AppDelegate
        appDelegate.foo()
    }
}


references:
https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/testing_with_xcode/chapters/04-writing_tests.html#//apple_ref/doc/uid/TP40014132-CH4-SW8