You were responding to Stefan. As such, it doesn’t matter whether you can imagine a test that works that way; it matters whether his uncertainty over whether the test works includes the possibility of it working that way.
Your example does not address this case—it’s about different tests producing different results.
If you don’t actually know that they freeze up at the sight of the number 8, and you are 50% likely to produce a test that contains the number 8, then the test has a 50% chance of working, by your own reasoning—actually, it has a 0% or 100% chance of working, but since you are uncertain about whether it works, you can fold the uncertainty into your estimate of how good the test is and claim 50%.
You were responding to Stefan. As such, it doesn’t matter whether you can imagine a test that works that way; it matters whether his uncertainty over whether the test works includes the possibility of it working that way.
If you don’t actually know that they freeze up at the sight of the number 8, and you are 50% likely to produce a test that contains the number 8, then the test has a 50% chance of working, by your own reasoning—actually, it has a 0% or 100% chance of working, but since you are uncertain about whether it works, you can fold the uncertainty into your estimate of how good the test is and claim 50%.