Before i head down this path, what are implications of fertility testing in terms of diagnostic ability and invasiveness of follow-up tests?

Depends on results: A full fertility workup checks the number of eggs left in your ovaries (ovarian reserve), tests for hormonal problems affecting fertility & problems with the uterus such as fibroids/ polyps. Hysterosalpingogram (hsg) test checks the fallopian tubes and uterine cavity . Semen analysis detects the 40-50% of male partners with sperm issues. The invasiveness of follow up depends on the initial results.

Good test accuracy: Fertility testing is much more accurate now than it was 20 years ago, when we did not know much about ovarian reserve testing. We used to say that 15-20% of couples had 'unexplained infertility' when all the tests came out normal, now it is way under 1% of couples who are really unexplained. However fertility tests are not perfect, couples with bad tests still conceive, some with good tests don't.