My son was sent for Fragile X testing. It's a genetic condition affecting the X chromosome. It's also the leading known genetic cause of autism. It is a spectrum diagnosis, it affects a wide variety of people at different stages of life. A simple blood test can confirm or rule out a diagnosis. I'd be happy to go into more detail about this if you're interested.

we had the microarray done. It checks all the chromosomes for deletions and duplications. My older daughter has a deletion that caused her developmental delays and my younger daughter has the same deletion, as well as a duplication.

The other most common test done is a chromosomal microarray test looking for abnormalities at the chromosome level (duplication, missing, etc.). There are about a dozen other genetic conditions that have high comorbidity with ASD and the tests for these are separate.