class RSpec::Matchers::BuiltIn::YieldProbe

def yielded_once?(matcher_name)
  case num_yields
  when 1 then true
  when 0 then false
  else
    raise "The #{matcher_name} matcher is not designed to be used with a " +
          "method that yields multiple times. Use the yield_successive_args " +
          "matcher for that case."
  end
end