The answer as to whether a DNA test can tell you your ethnic identity? Yes — and no.
We know that, when it comes to DNA, geography matters. Although in principle anyone can mate with anyone else, in practice we tend to mate with people nearby. If we could assemble all the DNA of everyone everywhere, we would expect to find that people living near each other were more likely to be genetically similar than people living farther apart.
Source: Can You Tell Your Ethnic Identity From Your DNA?
It would provide insight for those who have little to no family history. My family barely has any details beyond my grandparents, and even then – I discover that my parents have neglected to mention things.
In a significant boost for 23andMe, the Food and Drug Administration has allowed the direct-to-consumer genetics Silicon Valley startup to use its kit to test for a serious genetic disorder known as Bloom Syndrome.
In November 2013, the FDA ordered 23andMe to stop marketing and selling its kits as a way to test for genetic health information. This marks the first time the FDA has allowed for a home “carrier screening” genetic test. (Ars examined the state of direct-to-consumer genetic testing in April 2014.) Since the 2013 ban, 23andMe customers could only use the service as a way to find out more about their genealogy.
Source: FDA allows 23AndMe to use its genetic kits to test for Bloom Syndrome
While the ability to test for yourself can lead to quite some insight. From my own experience, discovering family medical history can be difficult. And given random mutation, it’s possible you might have something that wouldn’t be covered in family history.
Either way, watch Gattaca if you haven’t already.