Morning All!
Some things I noticed while playing with 3.1 master last night.
1) When using the #create! method on an association and pass "nil" vs an empty hash, now fails silently with no warning or anything. It's almost like a no-op. I did not test to see if this behavior occurred on a basic model or not. My app's controller was setup in such a way that I would always pass params[:foo] and sometimes that was nil and for years that has always worked. Does this sound patch worthy? If so I'll scrap some time up and see what happens.
2) I noticed that the Rails.backtrace_cleaner was not being used in my tests under 1.9.x since that uses MiniTest. This could have been happening for as long as there has been MiniTest usage since the backtrace cleaner was introduced, I may have never noticed before. Either way I created a plugin last night [1] called MiniBacktrace that is really just a few lines of code [2]. I'd be willing to submit a patch if you think this is helpful. I could easily check to see if the version of MiniTest supports the method chain interface to make this happen or take other advice. I found it really helpful 
[1] https://github.com/metaskills/mini_backtrace [2] https://github.com/metaskills/mini_backtrace/blob/master/lib/mini_backtrace/unit.rb
- Thanks, Ken