Rspec let scoping - ruby

Question

I believe I have a problem with rspec let and scoping. I can use the methods defined with let in examples (the "it" blocks), but not outside (the describe block where I did the let).
5 describe Connection do
8 let(:connection) { described_class.new(connection_settings) }
9
10 it_behaves_like "any connection", connection
24 end
When I try to run this spec, I get the error:
connection_spec.rb:10: undefined local
variable or method `connection' for
Class:0xae8e5b8 (NameError)
How can I pass the connection parameter to the it_behaves_like?

Answer 1

let() is supposed to be scoped to the example blocks and unusable elsewhere. You don't actually use let() as parameters. The reason it does not work with it_behaves_like as a parameter has to do with how let() gets defined. Each example group in Rspec defines a custom class. let() defines an instance method in that class. However, when you call it_behaves_like in that custom class, it is calling at the class level rather than from within an instance.
I've used let() like this:
shared_examples_for 'any connection' do
it 'should have valid connection' do
connection.valid?
end
end
describe Connection do
let(:connection) { Connection.new(settings) }
let(:settings) { { :blah => :foo } }
it_behaves_like 'any connection'
end
I've done something similar to bcobb's answer, though I rarely use shared_examples:
module SpecHelpers
module Connection
extend ActiveSupport::Concern
included do
let(:connection) { raise "You must override 'connection'" }
end
module ClassMethods
def expects_valid_connection
it "should be a valid connection" do
connection.should be_valid
end
end
end
end
end
describe Connection do
include SpecHelpers::Connection
let(:connection) { Connection.new }
expects_valid_connection
end
The definition of those shared examples are more verbose than using shared examples. I guess I find "it_behave_like" being more awkward than extending Rspec directly.
Obviously, you can add arguments to .expects_valid_connections
I wrote this to help a friend's rspec class: http://ruby-lambda.blogspot.com/2011/02/agile-rspec-with-let.html ...

Answer 2

Redacted -- completely whiffed on my first solution. Ho-Sheng Hsiao gave a great explanation as to why.
You can give it_behaves_like a block like so:
describe Connection do
it_behaves_like "any connection" do
let(:connection) { described_class.new(connection_settings) }
end
end

Answer 3

I've discovered that if you do not explicitly pass the parameter declared by let, it will be available in the shared example.
So:
describe Connection do
let(:connection) { described_class.new(connection_settings) }
it_behaves_like "any connection"
end
connection will be available in the shared example specs

Answer 4

I found what works for me:
describe Connection do
it_behaves_like "any connection", new.connection
# new.connection: because we're in the class context
# and let creates method in the instance context,
# instantiate a instance of whatever we're in
end

Answer 5

This works for me:
describe "numbers" do
shared_examples "a number" do |a_number|
let(:another_number) {
10
}
it "can be added to" do
(a_number + another_number).should be > a_number
end
it "can be subtracted from" do
(a_number - another_number).should be < a_number
end
end
describe "77" do
it_should_behave_like "a number", 77
end
describe "2" do
it_should_behave_like "a number", 2
end
end