You're right to test them. I'm too cheap to do so. When I first
began gardening, I got whatever was on sale. For annuals and
perennials, I dug top soil into the hard clay down to 12". I had a
triple mix that became crusty around mid-summer probably because of
all the salts in the manure portion of the mix.

For shrubs, I simply dug as deep as I could get, usually 24", and
filled it with top soil then planted my shrubs in the top soil. The
shrubs did great for a couple of years then it would sink into the
soil so I had to add more soil each year or take the shrub out and
replant it. I'd don't know if I'm imagining it but the top soil in
these pits seems to shrink.

Plants do beautifully in pure top soil. If your mix is light enough,
you might want to try it as a potting mix for outdoor plants too.