Is it possible to mock a function imported from a Swift package?

Question

I have written a simple Swift package called JwtApiClient that provides a few helper functions for making HTTP requests to JWToken-protected APIs that transfer data as JSON.

I am consuming one of these functions (postJsonDictionary) in another package:

import Foundation
import JwtApiClient

public func requestToken<T: Decodable>(
  _ username: String,
  _ password: String
) async throws -> T {
  let endpoint = "/users/login" // in the actual code this is an instance of URLComponents
                                // not String but it's irrelevant here
  let credentials = [
    "email": username,
    "password": password
  ]

  // I'd like to be able to mock this call
  return try await postJsonDictionary(endpoint!, credentials)
}

I was just wondering if it is possible to mock postJsonDictionary in a unit test to avoid making an underlying network request and to be able to assert on the parameters passed to it.

I have tried tricking my unit test into believing the function is a global but it doesn't work:

extension NSObject {
  public func postJsonDictionary<T: Decodable>(_ url: URL!, _ dictionary: [String: Any]) async throws -> T {
    try await Task.sleep(nanoseconds: 2 * 1_000_000_000)
    
    let fakeTokenResponse: TokenResponse = TokenResponse(token: "fake-token")
    
    return fakeTokenResponse as! T
  }
}

// XCTestCase below