Testing

Testing a view model

If you were testing load() on the view model below, which cases would you verify?

@MainActor @Observable
final class FeedViewModel {
    enum State { case idle, loading, loaded([Post]), failed(String) }
    private(set) var state: State = .idle
    private let repo: PostRepository
    init(repo: PostRepository) { self.repo = repo }
    func load() async {
        state = .loading
        do { state = .loaded(try await repo.fetch()) }
        catch { state = .failed(error.localizedDescription) }
    }
}

Your answer

Interviewer mode

See the short answer

Inject a stub repository and verify success (data in loaded), failure (the failed message), an empty array (loaded([])), and the transition into loading right after the call. Errors and empty responses are where the real bugs gather, so success alone isn't enough.

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Testing a view model

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