got the following error with Rpsec 2.10.0 :
/usr/local/rvm/gems/ruby-1.9.3-p194/gems/webmock-1.8.6/lib/webmock/rspec.rb:33:in `': uninitialized constant RSpec::Expectations::ExpectationNotMetError (NameError)
Adding require "rspec/expectations" will get rid of that error. Digging in to find out exactly why this came up, but it seems to be a rspec 2.9 -> 2.10 issue.
Fixed in master.