Custom Rspec matcher for checking class or module for constant. Based on a David Chelimsky's answer on StackOverflow.

have_constant.rb

# spec/support/matchers/have_constant.rb
 
RSpec::Matchers.define :have_constant do |constant|
  match do |owner|
    ([Class, Module].include?(owner.class) ? owner : owner.class).const_defined?(constant)
  end
 
  failure_message_for_should do |klass|
    "expected #{klass} to have constant #{constant}"
  end
 
  failure_message_for_should_not do |klass|
    "expected #{klass} not to have constant #{constant}"
  end
end