class RSpec::Matchers::BuiltIn::ContainExactly::PairingsMaximizer

def best_solution_for_pairing(expected_index, actual_index)
  modified_expecteds = apply_pairing_to(
    solution.indeterminate_expected_indexes,
    expected_to_actual_matched_indexes, actual_index)
  modified_expecteds.delete(expected_index)
  modified_actuals = apply_pairing_to(
    solution.indeterminate_actual_indexes,
    actual_to_expected_matched_indexes, expected_index)
  modified_actuals.delete(actual_index)
  solution + self.class.new(modified_expecteds, modified_actuals).find_best_solution
end