How to define Rspec custom matcher for its(:field) - ruby-on-rails

Question

I want to declare custom matcher for Rspec 2
I am using rspec 2.13 and rails 3.2.13.
I have tried to write something like this:
RSpec::Matchers.define :be_present do |expected|
match do
expected !be_empty
end
end
but when I use this in spec, it doesn't works
Failures:
1) NewsletterMailer.send_newsletter_to_groups from
Failure/Error: its(:from) { should be_present }
ArgumentError:
wrong number of arguments (1 for 0)
Spec code:
describe NewsletterMailer do
describe '.send_newsletter_to_emails' do
let(:user) { create(:admin) }
let(:user2) { create(:user) }
subject { NewsletterMailer.send_newsletter_to_emails(newsletter.id, "#{user.email}, #{user2.email}") }
its(:to) { should == [user.email, user2.email] }
its(:from) { should be_present }
its(:subject) { should be }
end
Edit:
I want to have reverse of logic like this:
its(:from) { should_not be_nil }

Answer 1

I'm not sure why you need a custom matcher at all here. Wouldn't
its(:from) { should be }
work for you?
See here:
https://www.relishapp.com/rspec/rspec-expectations/v/2-3/docs/built-in-matchers/be-matchers#be-matcher
obj.should be # passes if obj is not nil
Update:
Since apparently the question is how to write a custom matcher for an existing predicate present?, then the answer is: rspec already provides that, and there is still no need to write a custom matcher.
https://www.relishapp.com/rspec/rspec-expectations/v/2-3/docs/built-in-matchers/predicate-matchers
For any predicate #foo? on an object, you can just write should be_foo. Rspec will even define matchers for predicates that start with "has" like has_foo? with a more natural syntax, so that you can just write should have_foo.

Answer 2

Solution:
RSpec::Matchers.define :be_present do |expected|
match do |actual|
actual && actual.present?
end
end
Looks like this helper already exists in Rspec.
I just reinvented wheel. But I will still let this answer and don't delete this post.
It will be tip for developers, how to declare custom matcher without parameter eg.
be_something_special