MVVM & ViewController Specs

ViewController.swift

import Combine

class ViewController: UIViewController {
    @IBOutlet weak var label: UILabel!

    @IBOutlet weak var buttonUser: UIButton!
    @IBOutlet weak var buttonPosts: UIButton!

    var cancel = Set<AnyCancellable>()

    var viewModel = ViewModel()

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func getUsers() {
        self.handle(publidher: viewModel.fetch(action: .users))
    }

    @IBAction func getPosts() {
        self.handle(publidher: viewModel.fetch(action: .posts))
    }
}

extension ViewController {
    private func handle(publidher: AnyPublisher<String, Never>) {
        return publidher
            .receive(on: RunLoop.main)
            .assign(to: \.text!, on: self.label)
            .store(in: &cancel)
    }
}

ViewControllerSpec.swift

class FakeViewModel: ViewModel {
    override func fetch(action: ViewModel.Action) -> AnyPublisher<String, Never> {
        switch action {
        case .posts:
            return Just<String>("fakeposts").eraseToAnyPublisher()
        case .users:
            return Just<String>("fakeusers").eraseToAnyPublisher()
        }
    }
}

class ViewControllerSpec: XCTestCase {
    var subject: ViewController?

    func testUserButtonAction() {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let sut = storyboard.instantiateViewController(identifier: "ViewController") as! ViewController
        _ = sut.view

        sut.viewModel = FakeViewModel()
        sut.buttonUser.sendActions(for: .touchUpInside)
        let delayExpectation = XCTestExpectation()
        delayExpectation.isInverted = true
        wait(for: [delayExpectation], timeout: 1)
        XCTAssertTrue(sut.label.text == "fakeusers", "should be same as publisher")
    }

    func testPostButtonAction() {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let sut = storyboard.instantiateViewController(identifier: "ViewController") as! ViewController
        _ = sut.view

        sut.viewModel = FakeViewModel()
        sut.buttonPosts.sendActions(for: .touchUpInside)
        let delayExpectation = XCTestExpectation()
        delayExpectation.isInverted = true
        wait(for: [delayExpectation], timeout: 1)

        XCTAssertTrue(sut.label.text == "fakeposts", "should be same as publisher")
    }

}

Viewmodel.swift

import Foundation
import Combine

class ViewModel {
    private let interator: Interactor

    init() {
        self.interator = Interactor()
    }

    func fetch(action: Action) -> AnyPublisher<String, Never> {
        return interator.fetch(action: action)
    }
}

extension ViewModel {

    enum Action {
        case users
        case posts
    }

    private class Interactor {
        // calling api or some heavy stuff and modify return type
        func fetch(action:  Action) -> AnyPublisher<String, Never>  {
            switch action {
            case .posts:
                return Just<String>("posts....")
                    .eraseToAnyPublisher()

            case .users:
                return Just<String>("users....")
                    .delay(for: .seconds(1), scheduler: RunLoop.main)
                    .eraseToAnyPublisher()
            }
        }
    }
}

ViewModelSpec.swift

import Combine

class ViewModelSpec: XCTestCase {

    func testViewModelFetchUsers() {
        let viewModelodel:  ViewModel = FakeViewModel()
        var userText = ""
        let expectation = self.expectation(description: "user")
        _  = viewModelodel.fetch(action: .users).sink { (str) in
            userText = str
            expectation.fulfill()
        }
        waitForExpectations(timeout: 2)
        XCTAssertTrue(userText == "fakeusers", "should be same as publisher")
    }

    func testViewModelFetchPosts() {
        let viewModelodel: ViewModel = FakeViewModel()
        var userText = ""
        let expectation = self.expectation(description: "posts")
        _  = viewModelodel.fetch(action: .posts).sink { (str) in
            userText = str
            expectation.fulfill()
        }
        waitForExpectations(timeout: 2)
        XCTAssertTrue(userText == "fakeposts", "should be same as publisher")
    }
    
}