Swift Test: Controlling moc api client behaviour

I am writing test for my project and declared a remote API client protolcol:

public protocol ApiClient {
    func load(completion: @escaping ([Any]?, String?))
}

and defined a moc api client that confirms to ApiClient:

class MocApiClient: ApiClient {
    func loadFlights(completion: @escaping ([Any]?, String?)) {
        // Load a sample JSON file and return it as response
    }
}

this way I am able return a response by loading a JSON file. This is the happy path of the test. After it I started to think about testing different possible response types and decided that I should be able to alter behaviour of the MocApiClient and defined this:

enum TestPath {
    case success
    case failure
}

and using it with MocApiClient:

class MocApiClient: ApiClient {

    var path: TestPath = .success

    func load(completion: @escaping ([Any]?, String?) -> Void) {

        switch path {
        case .success:
            completion([...], nil)
        case .failure:
            completion(nil, "error message")
        }
    }
}

Doyu think this is a good solution? Do you have any beter approachs?