If my tests fail, TC still publishes the NuGet packages.
I raised this is an issue with JetBrains, and was told it was a feature request. And, that as a workaround, I could split my builds in two and separate the publish step from the rest of the build.
As far as I’m concerned, this is a showstopper bug. It introduces broken behaviour out of the box, which you won’t find out about until you realise a broken package is in use downstream. If JetBrains expects people to use TeamCity as a NuGet feed, this needs to be fixed.
(There’s also no (easy) way to remove packages from the feed, but I’m less concerned about that :) )