Rspec&Cucumber test failures 'stack level too deep' after upgrading to Rails 4

Rspec&Cucumber test failures 'stack level too deep' after upgrading to
Rails 4

I have a Rails application that was working fine with Rails 3.2.14. I have
just started to work on upgrading it to Rails 4, essentially following
along with Railscast episode 415.
I got as far as the part where I try to run my rspec tests to find many
now fail with the following error:
Failure/Error: Unable to find matching line from backtrace
SystemStackError:
stack level too deep
I also checked my Cucumber tests and find similar failures.
stack level too deep (SystemStackError)
As everything was fine before I started upgrading, I have been searching
for other experiences that are similar but haven't found any.
I have tried both Ruby 1.9 and 2.0. I have not modified any code
Any guidance appreciated.