> My question is basically: what needs to be done so that 
> https://tracker.debian.org/pkg/rust-event-listener 
> <https://tracker.debian.org/pkg/rust-event-listener> can actually 
> migrate testing?
Good question. It seems that britney2 did schedule some combination 
"correctly", but not all. That is probably due to the order in which 
packages were uploaded. I.e. if a package needs some other package, 
britney2 will schedule the test for both triggers and if it passes, it 
counts for both. However, if the dependent-on package is later updated 
again, britney2 doesn't see the relation and will not schedule the 
combination. If the test than fails, the package is blocked. If there 
would be a versioned Breaks (not sure if the package is really broken, 
or merely the test, then a Breaks is a bit overkill), than britney2 
would again trigger the combination.
Does this help to tell the right answer? If this is only a test issue, 
and not really a versioned Breaks missing, I'm willing to manually 
trigger the right test combination. But then people need to hold off 
with uploading, otherwise the results might come too late.
I honestly wish I could tell. The autopkgtest output remains rather mysterious to me.
Maybe I should be looking elsewhere in addition? But then at what? Britney's
update_output.gz?