Spy injections for unit testing

[kafejo]

Hi there, we are considering using Factory for our project and I'm trying to understand the best approach for testing dependent services callbacks. Imagine this scenario:

extension Container {
    var myService: Factory<MyService> {
        DefaultMyService()
    }
}

protocol MyService {
    func doSomething()
}

class DefaultMyService: MyService {
      func doSomething() {
           //  do something important here
      }
}

class MyClass {
     @Injected(\.myService) var myService

     func serviceCall() {
           myService.doSomething()
     }
}

Then in my test case I would do

class MyServiceSpy: MyService {
      var doSomethingCount = 0
      func doSomething() {
           doSomethingCount += 1
      }
}

extension Container {
     func setupMocks() {
          myService.context(.test) { MyServiceSpy() }
     }
}

class MyClassTests: XCTestCase { 
     func setUp() {
            super.setUp()
            Container.setupMocks()
     }

     func testServiceIsCalled() {
             let sut = MyClass()
             sut.serviceCall()

            let spyService = Container.shared.myService() as! MyServiceSpy  // This will resolve a new instance of MyServiceSpy
            XCTAssertEqual(spyService.doSomethingCount, 1) // This will fail 
     }
}

Can someone advise on what's generally the best approach here? Thanks!

[hmlongco]

a) I'd advise doing myService.context(.test) { MyServiceSpy() } in setup() or in testServiceIsCalled(). You're only going to be able to define the extension with that name once.

b) Doing let spyService = Container.shared.myService() resolves a new instance and is not the one injected when MyClass was created.