Test.swift

func testErrorAndThenSucceed() {
      let divisor = DivisorMock()
      let vm = ViewModel(divisor: divisor.divide)
  
      vm.load()
      // nah ini kan gagal hit pertama
      // ini ga perlu dites kan?
      vm.load()
  
      //anggap func .start return Result<Double, Error>
      XCTAssertThrowsError(try vm.start().get())
}

class DivisorMock {
private var calledCount = 0
func divide(val1: Int, val2: Int) throws -> Double {
      calledCount += 1
   if (calledCount % 2 == 0) {
      throw NSError()
   } else { return 2 }
}

}