FWIW, After I'd seen the first few clueless MDs I gave up on testing. Even cortiosol tests never registered the upside-down nature of my cycles and my distress. John Lowe cut me loose from paying any attention to thyroid tests.
I did test for toxic metals and prior to starting on some Yasko formulas, opted for a test which wasn't what had been suggested, but showed me I had SIBO. Even those, in retrospect, were unnecessary: we pretty much all have those issues, and benefit by acting accordingly.
And I tested my genes, which gave me me a roadmap for moving forward. Yet, in retrospect, the biggest gain I got from my 23andme test was a graphic representation of everything that had been wrong w/ my life. Ultimately even this test was less important than treating myself by the symptoms that arose as I progressed.
When I took the pyroluria questionnaire, I found another snapshot of life-long ailments, and began supplementing appropriately. Once I started tracking my symptoms, I uncovered the histamine and sulfur intolerances, and could rectify/manage them. And following symptoms has been critical in managing B12/folate. Self-testing has been my guide for supps and dosages. This is how I've inched forward over the past 2.5 years, not from any test ordered by an MD.
OK, a more prudent addition. Testing for viruses is probably a good thing to do. Testing for Lyme, which is now appearing in epidemic numbers, is very tricky to get reliable results, and treating AS IF you have Lyme is in line w/ intelligent detoxification. Basic thyroid tests, including reverse T3 is probably a good idea, but you generally won't get that unless there's some previous thyroid issue. I'm sure there are some others. But all that I've been tested for was useless.