I think this is a better self-test.
Visualize a ball on a table. Now imagine someone walks up to the table, and gives the ball a push. What happens to the ball?
Now, answer these questions:
- What color was the ball?
- What gender was the person that pushed the ball?
- What did they look like?
- What size is the ball? Like a marble, or a baseball, or a basketball, or something else?
- What about the table, what shape was it? What is it made of?
And now the important question: Did you already know, or did you have to choose a color/gender/size, etc. after being asked these questions?
This is an interesting one and I just tried it. I could answer all the questions about the ball, but none about the person or the table other than them existing in a hand-wavy sense. But rather than informing any level of aphantasia, it seems more likely that I simply did not prioritize visualizing those other things past their rough properties, focusing instead on the ball.
I could answer "the ball probably rolls off the table" and to everything else; I had no answer and would have to choose after the fact if pushed for an answer.
That's a test of how interested you are in random people, or indeed in visualizing things at all when not actually necessary.
You might need to take a person's background into account as well.
I, for instance, am an avid billiards player. A "ball on a table" naturally makes me think of a billiard ball on a billiards table. A whole host of detail was filled in for me, but all specifically in that context. I could answer some of the answers as if I could visualize, but most of them as someone who could not.
n = 1, I know, but sometimes it takes only one example.