According the answer I can use the rspec expectation form with the cucumber.
value = true
expect(value).to be_a(TrueClass) # => true
but if I use #be_true method it refused answering with exception:
expect(true).to be_true # => RSpec::Expectations::ExpectationNotMetError: expected true to respond to `true?`
So I can't use the method like I've used it in rails but without rails itself. So question is how can I add the methods not including the rails, and not defining them manually?