Can you do test setup before application loads in Swift? - swift

Question

I am a Swift/MacOS newbie working on a MacOS application does some setup involving keychain access and API calls in the viewDidLoad() methods in the main ViewController.
I am working on unit tests for my models, so I don't need and in fact do not want the code in viewDidLoad() to run. However, from what I can tell, the app gets loaded and those methods run before the test case setup() method, so I don't know how I could do any mocking or other actions.
I am using Xcode 11.5 and Swift 5.

Answer 1

One way to do it would be to have an separate NSApplicationMain for when unit tests are run vs one for "normal" runs.
First remove the #NSApplicationMain annotation from your current AppDelegate class. It should end up looking something like this:
AppDelegate.swift
import AppKit
class AppDelegate: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(_ aNotification: Notification) {
print("Debug/Production run")
// Insert code here to initialize your application
}
func applicationWillTerminate(_ aNotification: Notification) {
// Insert code here to tear down your application
}
}
Now create a new file called AppDelegateUnitTesting.swift and it's source should look like this:
AppDelegateUnitTesting.swift
import Foundation
import Cocoa
class AppDelegateTesting: NSObject, NSApplicationDelegate {
func applicationDidFinishLaunching(_ aNotification: Notification) {
print("Unit Testing Run")
// Insert code here to initialize your application
}
func applicationWillTerminate(_ aNotification: Notification) {
// Insert code here to tear down your application
}
}
Now add a new file called main.swift this file will determine in which environment our app is running, the source should be something like this:
main.swift
import Foundation
import Cocoa
let isRunningTests = NSClassFromString("XCTestCase") != nil &&
ProcessInfo.processInfo.arguments.contains("-XCUnitTests")
fileprivate var delegate: NSApplicationDelegate?
if !isRunningTests {
delegate = AppDelegate()
NSApplication.shared.delegate = delegate
// See this Answer to initialize the Windows programmatically
// https://stackoverflow.com/a/44604229/496351
} else {
delegate = AppDelegateTesting()
NSApplication.shared.delegate = delegate
}
NSApplication.shared.run()
To determine whether it's running in a Unit Test environment it checks if it can load the XCTestClass (which is only injected when testing) and it checks for the presence of the -XCUnitTest command line argument, we have to set this argument ourselves as part of the Scheme's Test action as shown in the image below
After doing all of this, you should see the message "Debug/Production run" printed when you press the play button and you should see the message "Unit Testing Run" printed whenever you run your unit tests.
You'll most likely have to add code to load the initial window programmatically this other answer shows how to do it:
how to Load initial window controller from storyboard?