di-2.swift

class MockBookService: BookService {
    func fetchPopularBooks(then handler: (Books) -> Void) {
        let books = [
            Book(id: "1", name: "X", author: "X"),
            Book(id: "2", name: "Y", author: "Y"),
            Book(id: "3", name: "Z", author: "Z")
        ]
        handler(books)
    }

    func fetchRelatedBooks(then handler: (Books) -> Void) {
        let books = [
            Book(id: "4", name: "A", author: "A"),
            Book(id: "5", name: "B", author: "B"),
            Book(id: "6", name: "C", author: "C")
        ]
        handler(books)
    }
}

class MockAuth: Auth {
    var isAuthenticated: Bool {
        return Bool.random()
    }
}