I am so sorry to hear about your dad. My dad had ALS and I also worked in Neurology so I have a pretty solid understanding of the diagnostic process, although I am not a physician. The diagnostic process is one of the most difficult periods for family members, I remember the frustration. Yes, it is very very common for a lengthy testing and waiting process to diagnose ALS. The reason for this is that ALS is a rule out diagnosis. That is, a neurologist does not give this diagnosis unless all other explanations have been ruled out. Unfortunately there is no specific test that says "yes this is ALS," its more like this test suggests it could be ALS but it could also be X, Y, or Z. Once the doctor can confirm it is not X, Y, or Z then they can diagnose ALS. The process does vary person to person especially depending on how advance their symptoms are and whether their personal case is complicated. For my dad his case was complicated because he had several other health problems that could have also caused his symptoms, but after a lengthy process of testing and waiting and testing and waiting we did finally get the diagnosis which I remember very clearly as both incredibly emotionally painful but also relieving that we finally knew what was going on and that process was over. I looked back and it looks like it took nearly 2 years for his diagnosis, though this is longer than normal I believe because of his complex medical history. My best advice to you is to keep advocating for your father as you have. Make sure to self-care through this stressful time. Don't hesitate to get a second opinion if you're not getting answers. I literally had a general neurologist send my father home with a wheelchair and no diagnosis and no plans to pursue a diagnosis and I had to fight for him to get the testing necessary for diagnosis. So, as frustrating and difficult it is, just keep in mind that if your dad's doctor is continuing with more tests its a good sign and that the doctor is not just throwing their hands up in the air and not pursing answers for him. Also, make sure your dad is seeing a neuromuscular specialist if not already, a general neurologist may not be qualified enough. Lastly, if possible, have extra support for yourself as you go through the diagnosis process with your dad. I clearly remember how hard the day was when we got the news. I hope the best for your dad and hope it's not ALS. Regardless sending you warm wishes and positive vibes.