Swift unit test cannot change the data to test the function

Question

I am applying unit test in viewController. Call the viewController and viewModel and try to change value to test different validation. However, when i change the value in unit test, the function "validateSalutation" in viewController cannot print the update value (i can directly change the value inside function, but cannot do it in unit test).

I am wondering how to do a unit test like these..... also the unit test for private method. Please Help

import XCTest

@testable myProject

class RegFormViewControllerTests: XCTestCase {
   var formEditviewModel: RegFormViewModel!
   var formEditController: RegFormViewController!

   override func setUp() {
       formEditviewModel = RegFormViewModel()
       formEditController = RegFormViewController(
            viewModel: formEditviewModel
        )
   }

     func test_isSalutationValid() {
        formEditviewModel.salutationInputViewModel.inputValue = "Miss"

         // I can print the value "Miss" here,  but in the function "validateSalution", i cannot see the updated value

        var result = formEditController.validateSalutation()
        XCTAssertFalse(result)
     }

}

class RegFormViewController: UIViewController {
 var formEditviewModel: RegFormViewModel!
 func validateSalutation() -> Bool {
         var isValid = false
         let salutation = formEditviewModel.salutationInputViewModel.inputValue
          
         print(salutation) // it is empty also when i change the value in unit test call this function

         if (!salutation.isEmpty) {
            isValid = true
         }

         return isValid
     }
}