Should validate_numericality_of with greater_than_or_equal_to

Testing RSpec
1

Hello,
I have this in my spec
it { should
validate_numericality_of(:amount).greater_than_or_equal_to(0) }

but I get error:

Failure/Error: it { should
validate_numericality_of(:amount).greater_than_or_equal_to(0) }
NoMethodError:
undefined method `greater_than_or_equal_to’ for
#RSpec::Matchers::Matcher:0xef23150

this page
http://remarkable.rubyforge.org/activerecord/classes/Remarkable/ActiveRecord/Matchers.html
has method
it { should validate_numericality_of(:age).only_integer }

and :less_than_or_equal_to is a valid option…

I am confused. How do I spec this? thanks.