Die Präsentationsebene testen

Intro to Presentation Layer Testing

Why Decouple UI Logic Tests?

What to Test: Presenters & View Models

Unit Testing Presenter Logic

Presenter Structure Example

/* User.java */
class User {
  String name;
  User(String name) { this.name = name; }
  String getName() { return name; }
}

/* UserResponse.java (from Use Case) */
class UserResponse {
  User user;
  UserResponse(User user) { this.user = user; }
  User getUser() { return user; }
}

/* UserViewModel.java (for UI) */
class UserViewModel {
  String displayName;
  UserViewModel(String name) { this.displayName = name; }
  String getDisplayName() { return displayName; }
}

/* UserView.java (interface for UI) */
interface UserView {
  void displayUser(UserViewModel viewModel);
}

/* UserPresenter.java */
class UserPresenter {
  private UserView view;
  UserPresenter(UserView view) { this.view = view; }

  void presentUser(UserResponse response) {
    String userName = response.getUser().getName();
    UserViewModel viewModel = new UserViewModel("Welcome, " + userName + "!");
    view.displayUser(viewModel);
  }
}

Testing a Basic Presenter

/* User.java (omitted for brevity, see previous scene) */
/* UserResponse.java (omitted for brevity) */
/* UserViewModel.java (omitted for brevity) */
/* UserView.java (omitted for brevity) */
/* UserPresenter.java (omitted for brevity) */

public class Main {
  public static void main(String[] args) {
    System.out.println("--- Presenter Test Simulation ---");

    // 1. Prepare test data (input to Presenter)
    User mockUser = new User("Alice");
    UserResponse mockResponse = new UserResponse(mockUser);

    // 2. Create a mock for the view interface
    //    This mock will let us check if displayUser was called correctly.
    UserView mockView = new UserView() {
      @Override
      public void displayUser(UserViewModel viewModel) {
        System.out.println("Mock View received ViewModel: " + viewModel.getDisplayName());
        // 3. Assertions (in a real test framework)
        if (viewModel.getDisplayName().equals("Welcome, Alice!")) {
          System.out.println("✔ Presenter transformed data correctly!");
        } else {
          System.out.println("✖ Presenter transformation failed.");
        }
      }
    };

    // 4. Instantiate the Presenter with the mock view
    UserPresenter presenter = new UserPresenter(mockView);

    // 5. Execute the method under test
    presenter.presentUser(mockResponse);
  }
}

Validating View Model Data

View Model Structure Example

/* Product.java (raw data from domain) */
class Product {
  String name;
  double price;
  Product(String name, double price) {
    this.name = name;
    this.price = price;
  }
  String getName() { return name; }
  double getPrice() { return price; }
}

/* ProductViewModel.java (display data for UI) */
class ProductViewModel {
  String displayName;
  String displayPrice;

  ProductViewModel(Product product) {
    this.displayName = product.getName().toUpperCase();
    this.displayPrice = String.format("$%.2f", product.getPrice());
  }

  String getDisplayName() { return displayName; }
  String getDisplayPrice() { return displayPrice; }
}

Testing View Model Construction

/* Product.java (omitted for brevity, see previous scene) */
/* ProductViewModel.java (omitted for brevity) */

public class Main {
  public static void main(String[] args) {
    System.out.println("--- View Model Test Simulation ---");

    // 1. Prepare raw data (input to ViewModel constructor)
    Product product = new Product("Laptop", 1200.50);

    // 2. Instantiate the ViewModel
    ProductViewModel viewModel = new ProductViewModel(product);

    // 3. Assertions (in a real test framework)
    System.out.println("Checking ViewModel content:");
    boolean nameCorrect = viewModel.getDisplayName().equals("LAPTOP");
    boolean priceCorrect = viewModel.getDisplayPrice().equals("$1200.50");

    if (nameCorrect) {
      System.out.println("✔ Display Name: '" + viewModel.getDisplayName() + "' is correct.");
    } else {
      System.out.println("✖ Display Name: Expected 'LAPTOP', got '" + viewModel.getDisplayName() + "'.");
    }

    if (priceCorrect) {
      System.out.println("✔ Display Price: '" + viewModel.getDisplayPrice() + "' is correct.");
    } else {
      System.out.println("✖ Display Price: Expected '$1200.50', got '" + viewModel.getDisplayPrice() + "'.");
    }

    if (nameCorrect && priceCorrect) {
      System.out.println("All ViewModel transformations worked!");
    } else {
      System.out.println("Some ViewModel transformations failed.");
    }
  }
}

Mocking Dependencies for Isolation

Test Your Knowledge

Recap: Testing Presentation Logic