text: // The MIT License (MIT)
  //
  // Copyright (c) 2016 Howard Hinnant
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in all
  // copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  // SOFTWARE.
  
  #include "date.h"
  #include <cassert>
  #include <sstream>
  
  template <class T>
  void
  test(const std::string& in_fmt, const std::string& input,
       const std::string& out_fmt, const std::string& output)
  {
      using namespace date;
      std::istringstream in{input};
      T t;
      in >> parse(in_fmt, t);
      assert(!in.fail());
      auto s = format(out_fmt, t);
      assert(s == output);
  }
  
  int
  main()
  {
      using namespace date;
      test<year>("%Y", "2017", "%Y", "2017");
      test<month>("%m", "3", "%m", "03");
      test<day>("%d", "25", "%d", "25");
      test<year_month>("%Y-%m", "2017-03", "%Y-%m", "2017-03");
      test<year_month>("%y%m", "1703", "%Y-%m", "2017-03");
      test<month_day>("%m/%d", "3/25", "%m/%d", "03/25");
      test<weekday>("%w", "3", "%w", "3");
  }
  