Answer.swift

//
// Answer.swift
//
// Answer is useful for testing to avoid boilerplate code
//

enum TestError: Error {
    case someError
}

enum Answer {
    static func success<T>(_ data: T) -> AnyPublisher<T, Error> {
        Just(data)
            .setFailureType(to: Error.self)
            .eraseToAnyPublisher()
    }

    static func fail<T>(_ error: Error = TestError.someError) -> AnyPublisher<T, Error> {
        Fail<T, Error>(error: error)
            .eraseToAnyPublisher()
    }

    static func fail<T>(_ error: Error, _ type: T.Type) -> AnyPublisher<T, Error> {
        Fail<T, Error>(error: error)
            .eraseToAnyPublisher()
    }

    static func nothing<T>() -> AnyPublisher<T, Error> {
        Empty<T, Error>()
            .eraseToAnyPublisher()
    }
}

// For example:
//
// 1. We have a fake implementation for testing purpose with answer AnyPublisher
// final class FakeSearchHistoryUseCase: UseCase {
//    var answer = Answer.success([History].stub)
//
//    func callAsFunction(with query: String) -> AnyPublisher<[History], Error> {
//        answer
//    }
//}
//
// 2. Then we could use Answer.success() (as well as error(), nothing())
// func testHistorySearch() {
//     // Arrange
//     searchHistoryUseCase.answer = Answer.success(.stub)
//     // Act
//     viewModel.searchHistory = "test"
//     // Assert
//     XCTAssertEqual(viewModel.history, .stub)
// }