Easy to do Combine test

XCTestCase+Extension.swift

import Foundation
import Combine
import XCTest

extension XCTestCase {
    func awaitPublisher<P: Publisher>(
        _ publisher: P,
        timeout: TimeInterval,
        description: String,
        trigger: (() -> Void)? = nil,
        file: StaticString = #file,
        line: UInt = #line
    ) throws -> P.Output {
        var cancelable: AnyCancellable?
        var result: Swift.Result<P.Output, P.Failure>?
        let excep = expectation(description: description)
        cancelable = publisher.first().sink(receiveCompletion: {
            switch $0 {
            case .failure(let error):
                result = .failure(error)
            case .finished: break
            }
            excep.fulfill()
        }, receiveValue: {
            result = .success($0)
        })
        
        trigger?()
        
        wait(for: [excep], timeout: timeout)
        cancelable?.cancel()
        return try XCTUnwrap(result, "Awaited publisher did produce null output ",
                             file: file,
                             line: line).get()
    }
}