I am Scottish

Question

All my ancesters came from Scotland except one went to Ireland do I realy need a DNA test

Answer 1

The ethnicity estimates are actually the least interesting and reliable parts of DNA testing - in my experience, ethnicity estimates provided by different companies from the same DNA sample can be widely divergent.

But what an autosomal DNA test can do for you is to provide you with matches to others (up to 4th-6th cousins, in some cases even more distantly related) who share some of the same DNA with you. This can lead you to previously unknown relatives and their family branches, as well as (through determining your common ancestors with these relatives) confirm your own ancestry and perhaps resolve between different hypotheses for uncertain ancestors (if you know you had an ancestor Miller, let's say, but don't know which Miller, but  you have DNA matches with descendants of just one Miller, that would be good evidence that you, too, are descended from that Miller).

Answer 2

You might be interested in the Scotland Project and their Tartan Trail Team, which helps you learn about Scotland sources, as well as wikitree.  

Use the G2G Join for Scotland Project

Answer 3

I have yet to meet anyone who is 100% anything. In Scotland for example, you have Viking raiders and the English at the very least that could be a part of your heritage. Even if you have a well documented lines back 25 generations, there is no telling who married into your family and what their "ethnicity" was. While Autosomal DNA only goes back eight generations or so, it's the ones who came before that laid the ground work. At eight generations back, you would have over 1600 ancestors that would have all had to have been born to "100 percent Scottish" parents.

As has been mentioned, the "ethnicity" estimates by the various main companies do vary greatly. But the real "gold" in DNA testing being able validate your paper trail through as yet unknown 2nd, 3rd, 4th or 5th cousins that you are made aware of because of that test. I highly recommend testing just for that reason alone.

Hope this helps!