test.swift

// some shared services
protocol NetworkService: class {
    func get() -> Any
}

class TestnetworkService: NetworkService {
    func get() -> Any {
        return "GET IT"
    }
}

// server specific endpoints
protocol PersonDataEndpoint: class {
    init(networkService: NetworkService)
    func getPerson() -> Any
}

// impl 1
final class TestPersonDataEndpoint: PersonDataEndpoint {
    let networkService: NetworkService
    init(networkService: NetworkService) {
        self.networkService = networkService
    }

    func getPerson() -> Any {
        return "\(networkService.get()) -> Bob"
    }
}

// impl 2
final class OloPersonDataEndpoint: PersonDataEndpoint {
    let networkService: NetworkService
    init(networkService: NetworkService) {
        self.networkService = networkService
    }

    func getPerson() -> Any {
        return "\(networkService.get()) -> Ololo"
    }
}

// specific service wrapper
class PersonDataService {

    let provider: PersonDataEndpoint

    init(provider: PersonDataEndpoint) {
        self.provider = provider
    }

    func getPerson() -> Any {
        return provider.getPerson()
    }
}

// core
class Core {
    let networkService: NetworkService = TestnetworkService()
    let personDataService: PersonDataService

    init(personDataClass: PersonDataEndpoint.Type) {

        personDataService = PersonDataService(provider: personDataClass.init(networkService: networkService))
    }
}

// --
let core = Core(personDataClass: arc4random_uniform(2) == 1 ? OloPersonDataEndpoint.self : TestPersonDataEndpoint.self)
print(core.personDataService.getPerson())