método(localizado em app/helpers/application_helper.rb):

def check_url(url)
  return true if /^(?:(?:https\:\/\/))|(?:(?:http\:\/\/))/.match(url)
  return false
end

spec(localizado em spec/models/user_spec.rb):

describe "check_url" do
  include ActionView::Helpers
	it "should return false if url does not have http or https" do
		@user = FactoryGirl.create(:user)
		@user.website = "test-test.test.test"
		expect(check_url(@user.website)).to eql(false)
	end
	it "should return true if url does have http" do
		@user = FactoryGirl.create(:user)
		@user.website = "http://test-test.test.test"
		expect(check_url(@user.website)).to eql(true)
	end
	it "should return true if url does have https" do
		@user = FactoryGirl.create(:user)
		@user.website = "https://test-test.test.test"
		expect(check_url(@user.website)).to eql(true)
	end
end

erros(vindos do terminal):

1. User check_url should return false if url does not have http or https Failure/Error: expect(check_url(@user.website)).to eql(false)

   NoMethodError:
     undefined method `check_url' for #<RSpec::ExampleGroups::User::CheckUrl:0x000027ddbee628>
     Did you mean?  check_box
   # ./spec/models/user_spec.rb:56:in `block (3 levels) in <top (required)>'
   

2. User check_url should return true if url does have http Failure/Error: expect(check_url(@user.website)).to eql(true)

   NoMethodError:
     undefined method `check_url' for #<RSpec::ExampleGroups::User::CheckUrl:0x000027dec9fbe8>
     Did you mean?  check_box
   # ./spec/models/user_spec.rb:61:in `block (3 levels) in <top (required)>'
   

3. User check_url should return true if url does have https Failure/Error: expect(check_url(@user.website)).to eql(true)

   NoMethodError:
     undefined method `check_url' for #<RSpec::ExampleGroups::User::CheckUrl:0x000027ded48608>
     Did you mean?  check_box
   # ./spec/models/user_spec.rb:66:in `block (3 levels) in <top (required)>'