Spy injections for unit testing #242

kafejo · 2024-10-22T11:24:19Z

kafejo
Oct 22, 2024

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 · 2024-10-22T13:51:03Z

hmlongco
Oct 22, 2024
Maintainer

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.

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Spy injections for unit testing #242

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Spy injections for unit testing #242

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kafejo Oct 22, 2024

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hmlongco Oct 22, 2024 Maintainer

kafejo
Oct 22, 2024

hmlongco
Oct 22, 2024
Maintainer