Two simple Combine Operators to test the sequence of values a Combine Publisher emits.

TestCombinePublisher.swift

// Operators

extension Publisher where Self.Output: Equatable {
    public func test(equalTo expectation: [Self.Output]) -> AnyCancellable {
        self
            .assertNoFailure()
            .reduce([Self.Output](), { $0 + [$1] })
            .sink() { assert($0 == expectation) }
    }
    
    public func test(first: Int, equalTo expectation: [Self.Output]) -> AnyCancellable {
        self
            .assertNoFailure()
            .prefix(first)
            .reduce([Self.Output](), { $0 + [$1] })
            .sink() { assert($0 == expectation) }
    }
}


// Sample Code

enum State: Equatable {
    case idle
    case loading
    case loaded
    case error
}

struct ViewModel {
    let state = CurrentValueSubject<State, Never>(.idle)
    
    func viewDidLoad() {
        state.value = .loading
        // Loading data ...
        state.value = .loaded
    }
    
    func viewDidUnload() {
        state.send(completion: .finished)
    }
}


// Sample Tests

let vm = ViewModel()
vm.state.test(equalTo: [.idle, .loading, .loaded]).store(in: &cancellables)
vm.state.test(first: 2, equalTo: [.idle, .loading]).store(in: &cancellables)
vm.viewDidLoad()
vm.viewDidUnload()