XCTestCase+Await.swift

//
//  XCTestCase+Await.swift
//
//  Useful functions to test with Combine
//

import Combine
import XCTest

enum TestAwaitError: Error {
    case unexpectedResult
}

extension XCTestCase {
    func values<T: Publisher>(_ publisher: T) async throws -> [T.Output] {
        var result: [T.Output] = []

        for try await value in publisher.values {
            result.append(value)
        }

        return result
    }

    func value<T: Publisher>(_ publisher: T) async throws -> T.Output? {
        (try await values(publisher)).first
    }

    func error<T: Publisher>(_ publisher: T) async -> T.Failure where T.Failure == Error {
        do {
            _ = try await values(publisher)
        } catch let error {
            return error
        }

        return TestAwaitError.unexpectedResult
    }
}

//
// For example, we want to test some Use Case with fake Repository that returns Combine AnyPublisher
//
//@MainActor
//final class SearchDocumentUseCaseTests: XCTestCase {
//    private var repository: FakeDocumentsRepository!
//    private var useCase: SearchDocumentUseCase!
//
//    override func setUp() async throws {
//        repository = FakeDocumentsRepository()
//        useCase = SearchDocumentUseCase(repository: repository)
//    }
//
//    func testExecute() async throws {
//        // Arrange
//        repository.readAnswer = Answer.success(.stub)
//
//        // Act
//        let result = try await value(useCase(with: "test"))
//
//        // Assert
//        XCTAssertEqual(result, .stub)
//    }
//
//    func testExecuteError() async {
//        // Arrange
//        repository.readAnswer = Answer.fail()
//
//        // Act
//        let result = await error(useCase(with: "test"))
//
//        // Assert
//        XCTAssertEqual(result as? TestError, .someError)
//    }
//}