I am not to familiar with do it yourself test kits as the Medical facilities where I work uses a professional service when we suspect something foul in the air. We also do an annual air bourn air quality checks twice a year.
I put mold test kits in a search engine and cam up with several. I cannot recommend any of them but makes for good reading.
Try here to start.
MoldIf you see kits for free, there still is a charge to "Read" it and send you results. If it were I, I would use two different kits and compare results one to the other.
Air bourn test can be very expensive. A device is put in the area and room air is pulled through it. It has a sticky agar to grow anything it collects. After a couple of days, these is looked at under a microscope and counted.
Start by looking for damp areas. Possible roof leak or somewhere around the house near the ground. Mold can't grow if it is dry.
Are your basement wall plain or paneled. Water can leak in behind the paneling and start growing mold.
If you think testing for mold is expensive, wait until you see what it will cost to clean up.