rspec/rspec-core — pull request #582 by masarakki (2012-03-16 15:18:27+00:00)
Title: fix bug in memorize of subject in its method

i found a bug in its method.

define_method(:subject) do
@_subject ||= some_method
end

can't memory if some_method return false or nil.
so fix to use instance_variable_defined? instead of ||=

its simple code for testing it
https://gist.github.com/2050346