tl;dr If you're using unittest, make sure you have an upper-bound on the package version in your pubspec.yaml.
The new (unit)test package is almost ready and it's awesome.
The 0.12.0 release will be the migration point from unittest to test.
Folks who use unittest will be able to upgrade to 0.12.0 and will get an exported version of test. You'll notice some breaking changes and a lot of deprecations. All future work will happen in the test package, so you'll want to migrate eventually.
In the mean time, if you're not ready to migrate, make sure you don't end up with 0.12.0 accidentally.
You might wonder why your tests start acting weird.