Is use of generics valid in XCTestCase subclasses? - ios

Question

I have a XCTestCase subclass that looks something like this. I have removed setup() and tearDown methods for brevity:
class ViewControllerTests <T : UIViewController>: XCTestCase {
var viewController : T!
final func loadControllerWithNibName(string:String) {
viewController = T(nibName: string, bundle: NSBundle(forClass: ViewControllerTests.self))
if #available(iOS 9.0, *) {
viewController.loadViewIfNeeded()
} else {
viewController.view.alpha = 1
}
}
}
And its subclass that looks something like this :
class WelcomeViewControllerTests : ViewControllerTests<WelcomeViewController> {
override func setUp() {
super.setUp()
self.loadControllerWithNibName("welcomeViewController")
// Put setup code here. This method is called before the invocation of each test method in the class.
}
func testName() {
let value = self.viewController.firstNameTextField.text
if value == "" {
XCTFail()
}
}
}
In theory, this should work as expected -- the compiler doesn't complain about anything. But it's just that when I run the test cases, the setup() method doesn't even get called. But, it says the tests have passed when clearly testName() method should fail.
Is the use of generics a problem? I can easily think of many non-generic approaches, but I would very much want to write my test cases like this. Is the XCTest's interoperability between Objective-C and Swift the issue here?

Answer 1

XCTestCase uses the Objective-C runtime to load test classes and find test methods, etc.
Swift generic classes are not compatible with Objective-C. See https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/InteractingWithObjective-CAPIs.html#//apple_ref/doc/uid/TP40014216-CH4-ID53:
When you create a Swift class that descends from an Objective-C class, the class and its members—properties, methods, subscripts, and initializers—that are compatible with Objective-C are automatically available from Objective-C. This excludes Swift-only features, such as those listed here:
Generics
...
Ergo your generic XCTestCase subclass can not be used by XCTest.

Answer 2

Well, actually its totally doable. You just have to create a class that will be sort of test runner. For example:
class TestRunner: XCTestCase {
override class func initialize() {
super.initialize()
let case = XCTestSuite(forTestCaseClass: ViewControllerTests<WelcomeViewController>.self)
case.runTest()
}
}
This way you can run all your generic tests.

Answer 3

I got it working in a kind of hacky way with protocols & associated types:
import XCTest
// If your xCode doesn't compile on this line, download the lastest toolchain as of 30 november 2018
// or change to where Self: XCTestCase, and do it also in the protocol extension.
protocol MyGenericTestProtocol: XCTestCase {
associatedtype SomeType
func testCallRunAllTests()
}
extension MyGenericTestProtocol {
// You are free to use the associated type here in any way you want.
// You can constraint the associated type to be of a specific kind
// and than you can run your generic tests in this protocol extension!
func startAllTests() {
for _ in 0...100 {
testPrintType()
}
}
func testPrintType() {
print(SomeType.self)
}
}
class SomeGenericTestInt: XCTestCase, MyGenericTestProtocol {
typealias SomeType = Int
func testCallRunAllTests() {
startAllTests()
}
}
class SomeGenericTestString: XCTestCase, MyGenericTestProtocol {
typealias SomeType = String
func testCallRunAllTests() {
startAllTests()
}
}

Answer 4

This approach (https://stackoverflow.com/a/39101121/311889) no longer works. The way I did it in Swift 5.2 is:
class MyFileTestCase: XCTestCase {
override func run() {
let suite = XCTestSuite(forTestCaseClass: FileTestCase<MyFile>.self)
suite.run()
super.run()
}
// At least one func is needed for `run` to be called
func testDummy() { }
}