ConcreteTypeCheckers.hpp

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//                Copyright Oliver J. Rosten 2020.                //
// Distributed under the GNU GENERAL PUBLIC LICENSE, Version 3.0. //
//    (See accompanying file LICENSE.md or copy at                //
//          https://www.gnu.org/licenses/gpl-3.0.en.html)         //
 
#pragma once
 
#include "sequoia/TestFramework/FreeCheckers.hpp"
#include "sequoia/TestFramework/FileEditors.hpp"
#include "sequoia/TestFramework/FileSystemUtilities.hpp"
#include "sequoia/Core/Object/Factory.hpp"
#include "sequoia/FileSystem/FileSystem.hpp"
#include "sequoia/Streaming/Streaming.hpp"
 
#include <any>
#include <array>
#include <format>
#include <functional>
#include <memory>
#include <optional>
#include <tuple>
#include <variant>
 
namespace sequoia::testing
{
  template<class Char, class Traits>
  struct value_tester<std::basic_string_view<Char, Traits>>
  {
    using string_view_type = std::basic_string_view<Char, Traits>;
 
    template<class Allocator>
    using string_type      = std::basic_string<Char, Traits, Allocator>;
  private:
    using iter_type = typename string_view_type::const_iterator;
    using size_type = typename string_view_type::size_type;
 
    static void appender(std::string& mess, string_view_type sv, size_type pos, size_type count)
    {
      if constexpr(sizeof(char) >= sizeof(Char))
      {
        mess.append(sv.substr(pos, count));
      }
      else
      {
        if(pos > sv.size()) throw std::out_of_range{"pos out of range"};
        const auto end{count > sv.size() - pos ? sv.size() : pos + count};
        std::ranges::transform(sv.begin() + pos, sv.begin() + end, std::back_inserter(mess), [](Char c) { return static_cast<char>(c); });
      }
    }
 
    template<class Advisor>
    static auto make_advisor(std::string_view info, string_view_type obtained, string_view_type prediction, size_type pos, const tutor<Advisor>& advisor)
    {
      constexpr size_type defaultOffset{30}, defaultCount{60}, npos{string_view_type::npos};
      const auto sz{std::ranges::min(obtained.size(), prediction.size())};
 
      auto newlineBackwards{ [pos](string_view_type sv){ return pos < sv.size() ? sv.rfind('\n', pos) : npos; } };
 
      const auto loc{std::ranges::min(newlineBackwards(prediction), newlineBackwards(obtained))};
 
      const size_type offset{loc < npos ? std::ranges::min(defaultOffset, pos - loc) : defaultOffset};
 
      const auto lpos{pos < offset ? 0 :
                         pos < sz  ? pos - offset : sz - std::ranges::min(sz, offset)};
 
      struct message{ std::string mess; bool trunc{}; };
 
      auto make{
        [](string_view_type sv, size_type lpos) -> message {
          std::string mess{lpos > 0 ? "..." : ""};
 
          const bool newline{(lpos < sv.size()) && (sv[lpos] == '\n')};
          if(newline) mess.append("\\n");
 
          const auto rpos{sv.find('\n', lpos+1)};
          const auto count{rpos == npos ? defaultCount : rpos - lpos};
 
          if(newline && (count == 1))
          {
            mess.append("\\n");
          }
          else
          {
            if(newline) ++lpos;
            appender(mess, sv, lpos, count);
          }
 
          const bool trunc{lpos + count < sv.size()};
          if(trunc) mess.append("...");
 
          return {mess, trunc};
        }
      };
 
      const auto[obMess,obTrunc]{make(obtained, lpos)};
      const auto[prMess,prTrunc]{make(prediction, lpos)};
 
      const bool trunc{lpos > 0 || obTrunc || prTrunc};
      const auto message{append_lines(info,  trunc ? "Surrounding substring(s):" : "Full strings:",
                                      prediction_message(obMess, prMess))};
 
      if constexpr(std::invocable<tutor<Advisor>, Char, Char>)
      {
 
        return tutor{
          [message, advisor] (Char a, Char b) {
            auto m{message};
            return append_advice(m, {advisor, a, b});
          },
          "\n"
        };
      }
      else
      {
        return tutor{
          [message](const auto&, const auto&) { return message; },
          "\n"
        };
      }
    }
 
  public:
    template<test_mode Mode, class Advisor>
    static void test(equality_check_t, test_logger<Mode>& logger, string_view_type obtained, string_view_type prediction, const tutor<Advisor>& advisor)
    {
      auto iters{std::ranges::mismatch(obtained, prediction)};
 
      if((iters.in1 != obtained.end()) && (iters.in2 != prediction.end()))
      {
        const auto dist{std::ranges::distance(obtained.begin(), iters.in1)};
        auto adv{make_advisor("", obtained, prediction, dist, advisor)};
 
        const auto numLines{std::count(prediction.begin(), iters.in2, '\n')};
 
        const auto mess{
          [dist,numLines]() {
            std::string m{"First difference detected "};
            numLines > 0 ? m.append("on line ").append(std::to_string(numLines+1))
                         : m.append("at character ").append(std::to_string(dist));
 
            return m.append(":");
          }()
        };
 
        check(equality, mess, logger, *(iters.in1), *(iters.in2), adv);
      }
      else if((iters.in1 != obtained.end()) || (iters.in2 != prediction.end()))
      {
        auto checker{
          [&logger, obtained, prediction, &advisor](auto begin, auto iter, std::string_view state, std::string_view adjective){
            const auto dist{std::ranges::distance(begin, iter)};
            const auto info{std::string{"First "}.append(state).append(" character: ").append(display_character(*iter))};
            auto adv{make_advisor(info, obtained, prediction, dist, advisor)};
 
            const auto mess{append_lines("Lengths differ", std::string{"Obtained string is too "}.append(adjective))};
 
            check(equality, mess, logger, obtained.size(), prediction.size(), adv);
          }
        };
 
        if(iters.in2 != prediction.end())
        {
          checker(prediction.begin(), iters.in2, "missing", "short");
        }
        else if(iters.in1 != obtained.end())
        {
          checker(obtained.begin(), iters.in1, "excess", "long");
        }
      }
    }
 
    template<test_mode Mode, class Advisor, class Allocator>
    static void test(equivalence_check_t, test_logger<Mode>& logger, string_view_type obtained, string_type<Allocator> prediction, const tutor<Advisor>& advisor)
    {
      test(equality, logger, obtained, string_view_type{prediction}, advisor);
    }
  };
 
  template<class Char, class Traits, alloc Allocator>
  struct value_tester<std::basic_string<Char, Traits, Allocator>>
  {
    using string_type = std::basic_string<Char, Traits, Allocator>;
    using string_view_type = std::basic_string_view<Char, Traits>;
 
    template<test_mode Mode, class Advisor>
    static void test(equality_check_t, test_logger<Mode>& logger, const string_type& obtained, const string_type& prediction, tutor<Advisor> advisor)
    {
      using tester = value_tester<std::basic_string_view<Char, Traits>>;
 
      tester::test(equality_check_t{}, logger, string_view_type{obtained}, string_view_type{prediction}, std::move(advisor));
    }
 
    template<test_mode Mode, std::size_t N, class Advisor>
    static void test(equivalence_check_t, test_logger<Mode>& logger, const string_type& obtained, char const (&prediction)[N], tutor<Advisor> advisor)
    {
       using tester = value_tester<std::basic_string_view<Char, Traits>>;
 
       tester::test(equality_check_t{}, logger, string_view_type{obtained}, string_view_type{prediction}, std::move(advisor));
    }
 
    template<test_mode Mode, class Advisor>
    static void test(equivalence_check_t, test_logger<Mode>& logger, const string_type& obtained, std::basic_string_view<Char, Traits> prediction, tutor<Advisor> advisor)
    {
       using tester = value_tester<std::basic_string_view<Char, Traits>>;
 
       tester::test(equality_check_t{}, logger, string_view_type{obtained}, string_view_type{prediction}, std::move(advisor));
    }
  };
 
  template<class S, class T>
  struct value_tester<std::pair<S, T>>
  {
    template<class CheckType, test_mode Mode, class U, class V, class Advisor>
      requires (   std::is_same_v<std::remove_cvref_t<S>, std::remove_cvref_t<U>>
                && std::is_same_v<std::remove_cvref_t<T>, std::remove_cvref_t<V>>)
    static void test(CheckType flavour, test_logger<Mode>& logger, const std::pair<S, T>& value, const std::pair<U, V>& prediction, const tutor<Advisor>& advisor)
    {
      check_elements(flavour, logger, value, prediction, std::move(advisor));
    }
 
    template<class CheckType, test_mode Mode, class Advisor>
    static void test(equality_check_t, test_logger<Mode>& logger, const std::pair<S, T>& value, const std::pair<S, T>& prediction, const tutor<Advisor>& advisor)
    {
      check_elements(equality, logger, value, prediction, std::move(advisor));
    }
 
  private:
    template<class CheckType, test_mode Mode, class U, class V, class Advisor>
    static void check_elements(CheckType, test_logger<Mode>& logger, const std::pair<S, T>& value, const std::pair<U, V>& prediction, const tutor<Advisor>& advisor)
    {
      check(CheckType{}, "First element of pair is incorrect", logger, value.first, prediction.first, advisor);
      check(CheckType{}, "Second element of pair is incorrect", logger, value.second, prediction.second, advisor);
    }
  };
 
  template<class... T>
  struct value_tester<std::tuple<T...>>
  {
  private:
    template<std::size_t I = 0, class CheckType, test_mode Mode, class... U, class Advisor>
      requires (I < sizeof...(T))
    static void check_tuple_elements(CheckType flavour, test_logger<Mode>& logger, const std::tuple<T...>& value, const std::tuple<U...>& prediction, const tutor<Advisor>& advisor)
    {
      check(flavour, std::format("Element {} of tuple incorrect", I), logger, std::get<I>(value), std::get<I>(prediction), advisor);
      check_tuple_elements<I+1>(flavour, logger, value, prediction, advisor);
    }
 
    template<std::size_t I = 0, class CheckType, test_mode Mode, class... U, class Advisor>
    static void check_tuple_elements(CheckType, test_logger<Mode>&, const std::tuple<T...>&, const std::tuple<U...>&, const tutor<Advisor>&)
    {}
 
  public:
    template<class CheckType, test_mode Mode, class... U, class Advisor>
      requires ((sizeof...(T) == sizeof...(U)) && (std::is_same_v<std::remove_cvref_t<T>, std::remove_cvref_t<U>> && ...))
    static void test(CheckType flavour, test_logger<Mode>& logger, const std::tuple<T...>& value, const std::tuple<U...>& prediction, const tutor<Advisor>& advisor)
    {
      check_tuple_elements(flavour, logger, value, prediction, advisor);
    }
 
    template<class CheckType, test_mode Mode, class Advisor>
    static void test(equality_check_t, test_logger<Mode>& logger, const std::tuple<T...>& value, const std::tuple<T...>& prediction, const tutor<Advisor>& advisor)
    {
      check_tuple_elements(equality, logger, value, prediction, advisor);
    }
  };
 
  [[nodiscard]]
  std::string path_check_preamble(std::string_view prefix, const std::filesystem::path& path, const std::filesystem::path& prediction);
 
  struct string_based_file_comparer
  {
    template<test_mode Mode>
    void operator()(test_logger<Mode>& logger, const std::filesystem::path& file, const std::filesystem::path& prediction) const
    {
      const auto [reducedWorking, reducedPrediction] {get_reduced_file_content(file, prediction)};
 
      testing::check(report_failed_read(file),       logger, static_cast<bool>(reducedWorking));
      testing::check(report_failed_read(prediction), logger, static_cast<bool>(reducedPrediction));
 
      if(reducedWorking && reducedPrediction)
      {
        check(equality, path_check_preamble("Contents of", file, prediction), logger, reducedWorking.value(), reducedPrediction.value());
      }
    }
  };
 
  template<class T>
  inline constexpr bool is_file_comparer_v{
    std::invocable<T, test_logger<test_mode::standard>&, std::filesystem::path, std::filesystem::path>
  };
 
  template<class DefaultComparer, class... Comparers>
    requires (is_file_comparer_v<DefaultComparer> && (is_file_comparer_v<Comparers> && ...))
  class general_file_checker
  {
  public:
    [[nodiscard]]
    constexpr static std::size_t size() noexcept
    {
      return 1 + sizeof...(Comparers);
    }
 
    template<class... Extensions>
        requires (sizeof...(Extensions) == size()) && (std::is_constructible_v<std::string, Extensions> && ...)
    general_file_checker(Extensions... extensions)
      : m_Factory{std::move(extensions)...}
    {}
 
    template<test_mode Mode>
    void check_file(test_logger<Mode>& logger, const std::filesystem::path& file, const std::filesystem::path& prediction) const
    {
      const auto checker{m_Factory.template make_or<DefaultComparer>(file.extension().string())};
      std::visit([&logger, &file, &prediction](auto&& fn){ fn(logger, file, prediction); }, checker);
    }
  private:
    using factory = object::factory<DefaultComparer, Comparers...>;
 
    factory m_Factory;
  };
 
  template<class DefaultComparer, class... Comparers>
  using equivalence_with_bespoke_file_checker_t = general_equivalence_check_t<general_file_checker<DefaultComparer, Comparers...>>;
 
  template<class DefaultComparer, class... Comparers>
  using weak_equivalence_with_bespoke_file_checker_t = general_weak_equivalence_check_t<general_file_checker<DefaultComparer, Comparers...>>;
 
  template<>
  struct value_tester<std::filesystem::path>
  {
    template<class DefaultComparer, class... Comparers, test_mode Mode>
    static void test(equivalence_with_bespoke_file_checker_t<DefaultComparer, Comparers...> checker,
                     test_logger<Mode>& logger,
                     const std::filesystem::path& path,
                     const std::filesystem::path& prediction)
    {
      namespace fs = std::filesystem;
 
      auto pred{
        [&logger](const fs::path& pathFinalToken, const fs::path& predictionFinalToken)
        {
           return check(equality, "Final path token", logger, pathFinalToken, predictionFinalToken);
        }
      };
 
      check_path(logger, checker.customizer, path, prediction, pred);
    }
 
    template<test_mode Mode>
    static void test(equivalence_check_t, test_logger<Mode>& logger, const std::filesystem::path& path, const std::filesystem::path& prediction)
    {
      test(basic_path_equivalence, logger, path, prediction);
    }
 
    template<class DefaultComparer, class... Comparers, test_mode Mode>
    static void test(weak_equivalence_with_bespoke_file_checker_t<DefaultComparer, Comparers...> checker,
                     test_logger<Mode>& logger,
                     const std::filesystem::path& path,
                     const std::filesystem::path& prediction)
    {
      namespace fs = std::filesystem;
      check_path(logger, checker.customizer, path, prediction, [](const fs::path&, const fs::path&) { return true; });
    }
 
    template<test_mode Mode>
    static void test(weak_equivalence_check_t, test_logger<Mode>& logger, const std::filesystem::path& path, const std::filesystem::path& prediction)
    {
      test(basic_path_weak_equivalence, logger, path, prediction);
    }
  private:
    constexpr static std::array<std::string_view, 2>
      excluded_files{".DS_Store", ".keep"};
 
    constexpr static std::array<std::string_view, 1>
      excluded_extensions{seqpat};
 
    using basic_file_checker_t = general_file_checker<string_based_file_comparer>;
 
    static const basic_file_checker_t basic_file_checker;
 
    static const general_equivalence_check_t<basic_file_checker_t>      basic_path_equivalence;
    static const general_weak_equivalence_check_t<basic_file_checker_t> basic_path_weak_equivalence;
 
    template<test_mode Mode, class Customization, invocable_r<bool, std::filesystem::path, std::filesystem::path> FinalTokenComparison>
    static void check_path(test_logger<Mode>& logger, const Customization& custom, const std::filesystem::path& path, const std::filesystem::path& prediction, FinalTokenComparison compare)
    {
      namespace fs = std::filesystem;
 
      const auto pathType{fs::status(path).type()};
      const auto predictionType{fs::status(prediction).type()};
 
      if(check(equality, path_check_preamble("Path type", path, prediction), logger, pathType, predictionType))
      {
        if(!path.empty())
        {
          const auto pathFinalToken{back(path)};
          const auto predictionFinalToken{back(prediction)};
          if(compare(pathFinalToken, predictionFinalToken))
          {
            switch(pathType)
            {
            case fs::file_type::regular:
              check_file(logger, custom, path, prediction);
              break;
            case fs::file_type::directory:
              check_directory(logger, custom, path, prediction, compare);
              break;
            default:
              throw std::logic_error{std::string{"Detailed equivalance check for paths of type '"}
                .append(serializer<fs::file_type>::make(pathType)).append("' not currently implemented")};
            }
          }
        }
      }
    }
 
    template<test_mode Mode, class Customization, invocable_r<bool, std::filesystem::path, std::filesystem::path> FinalTokenComparison>
    static void check_directory(test_logger<Mode>& logger, const Customization& custom, const std::filesystem::path& dir, const std::filesystem::path& prediction, FinalTokenComparison compare)
    {
      namespace fs = std::filesystem;
 
      auto generator{
        [](const fs::path& dir) {
          std::vector<fs::path> paths{};
          for(const auto& p : fs::directory_iterator(dir))
          {
            if(    std::ranges::find(excluded_files,      p.path().filename())  == excluded_files.end()
                && std::ranges::find(excluded_extensions, p.path().extension()) == excluded_extensions.end())
            {
               paths.push_back(p);
            }
          }
 
          std::ranges::sort(paths);
 
          return paths;
        }
      };
 
      const std::vector<fs::path> paths{generator(dir)}, predictedPaths{generator(prediction)};
 
      check(equality, std::string{"Number of directory entries for "}.append(dir.generic_string()),
        logger,
        paths.size(),
        predictedPaths.size());
 
      const auto iters{std::ranges::mismatch(paths, predictedPaths,
          [&dir,&prediction](const fs::path& lhs, const fs::path& rhs) {
            return fs::relative(lhs, dir) == fs::relative(rhs, prediction);
          })};
      if((iters.in1 != paths.end()) && (iters.in2 != predictedPaths.end()))
      {
        check(equality, "First directory entry mismatch", logger, *iters.in1, *iters.in2);
      }
      else if(iters.in1 != paths.end())
      {
        check(equality, "First directory entry mismatch", logger, *iters.in1, fs::path{});
      }
      else if(iters.in2 != predictedPaths.end())
      {
        check(equality, "First directory entry mismatch", logger, fs::path{}, *iters.in2);
      }
      else
      {
        for(std::size_t i{}; i < paths.size(); ++i)
        {
          check_path(logger, custom, paths[i], predictedPaths[i], compare);
        }
      }
    }
 
    template<test_mode Mode, class Customization>
    static void check_file(test_logger<Mode>& logger, const Customization& custom, const std::filesystem::path& file, const std::filesystem::path& prediction)
    {
      custom.check_file(logger, file, prediction);
    }
  };
 
  template<class... Ts>
  struct value_tester<std::variant<Ts...>>
  {
    using type = std::variant<Ts...>;
 
    template<class CheckType, test_mode Mode, class Advisor>
    static void test(CheckType flavour, test_logger<Mode>& logger, const type& obtained, const type& prediction, tutor<Advisor> advisor)
    {
      if(check(equality, "Variant Index", logger, obtained.index(), prediction.index()))
      {
        check_value(flavour, logger, obtained, prediction, advisor, std::make_index_sequence<sizeof...(Ts)>());
      }
    }
  private:
    template<class CheckType, test_mode Mode, class Advisor, std::size_t... I>
    static void check_value(CheckType flavour, test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor, std::index_sequence<I...>)
    {
      (check_value<I>(flavour, logger, obtained, prediction, advisor), ...);
    }
 
    template<std::size_t I, class CheckType, test_mode Mode, class Advisor>
    static void check_value(CheckType flavour, test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor)
    {
      if(auto pObtained{std::get_if<I>(&obtained)})
      {
        if(auto pPrediction{std::get_if<I>(&prediction)})
        {
          check(flavour, "Variant Contents", logger, *pObtained, *pPrediction, advisor);
        }
        else
        {
          throw std::logic_error{"Inconsistant variant access"};
        }
      }
    }
  };
 
  template<class T>
  struct value_tester<std::optional<T>>
  {
    using type = std::optional<T>;
 
    template<class CheckType, test_mode Mode, class Advisor>
    static void test(CheckType flavour, test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor)
    {
      if(obtained && prediction)
      {
        check(flavour, "Contents of optional", logger, *obtained, *prediction, advisor);
      }
      else
      {
        const bool obtainedIsNull{obtained}, predictionIsNull{prediction};
 
        check(equality,
              nullable_type_message(obtainedIsNull, predictionIsNull),
              logger,
              static_cast<bool>(obtained),
              static_cast<bool>(prediction));
      }
    }
  };
 
  template<>
  struct value_tester<std::any>
  {
    using type = std::any;
 
    template<test_mode Mode, class T, class Advisor>
    static void test(equivalence_check_t, test_logger<Mode>& logger, const type& obtained, const T& prediction, const tutor<Advisor>& advisor)
    {
      if(check("Has value", logger, obtained.has_value()))
      {
        try
        {
          const auto& val{std::any_cast<T>(obtained)};
          check(with_best_available, "Value held by std::any", logger, val, prediction, advisor);
        }
        catch(const std::bad_any_cast&)
        {
          check("std::any does not hold the expected type", logger, false);
        }
      }
    }
  };
 
  template<class T>
  struct value_tester<T*>
  {
    using type = T*;
 
    template<test_mode Mode, class Advisor>
    static void test(equivalence_check_t, test_logger<Mode>& logger, type obtained, type prediction, const tutor<Advisor>& advisor)
    {
      if(obtained && prediction)
      {
        check(with_best_available, "Pointees differ", logger, *obtained, *prediction, advisor);
      }
      else
      {
        const auto obtainedIsNull{static_cast<bool>(obtained)}, predictionIsNull{static_cast<bool>(prediction)};
 
        check(equality,
              nullable_type_message(obtainedIsNull, predictionIsNull),
              logger,
              obtainedIsNull,
              predictionIsNull);
      }
    }
  };
 
  template<class T>
  struct smart_pointer_tester
  {
    using type = T;
 
    template<test_mode Mode, class Advisor>
    static void test(equality_check_t, test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor)
    {
      check(equality, "Underlying pointers differ", logger, obtained.get(), prediction.get(), advisor);
    }
  protected:
    ~smart_pointer_tester() = default;
 
    template<test_mode Mode, class Advisor>
    static void test_pointees(test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor)
    {
      if(obtained && prediction)
      {
        check(with_best_available, "Pointees differ", logger, *obtained, *prediction, advisor);
      }
      else
      {
        const bool obtainedIsNull{obtained}, predictionIsNull{prediction};
 
        check(equality,
              nullable_type_message(obtainedIsNull, predictionIsNull),
              logger,
              static_cast<bool>(obtained),
              static_cast<bool>(prediction));
      }
    }
  };
 
  template<class T>
  struct value_tester<std::unique_ptr<T>> : smart_pointer_tester<std::unique_ptr<T>>
  {
    using type = std::unique_ptr<T>;
    using base_t = smart_pointer_tester<std::unique_ptr<T>>;
    using base_t::test;
 
    template<test_mode Mode, class Advisor>
    static void test(equivalence_check_t, test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor)
    {
      using base_t = base_t;
      base_t::test_pointees(logger, obtained, prediction, advisor);
    }
  };
 
  template<class T>
  struct value_tester<std::shared_ptr<T>> : smart_pointer_tester<std::shared_ptr<T>>
  {
    using type = std::shared_ptr<T>;
    using base_t = smart_pointer_tester<std::shared_ptr<T>>;
    using base_t::test;
 
    template<test_mode Mode, class Advisor>
    static void test(equivalence_check_t, test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor)
    {
      base_t::test_pointees(logger, obtained, prediction, advisor);
    }
  };
 
  template<class T>
  struct value_tester<std::weak_ptr<T>>
  {
    using type = std::weak_ptr<T>;
 
    template<test_mode Mode>
    static void test(equality_check_t, test_logger<Mode>& logger, const type& obtained, const type& prediction)
    {
      check(equality, "Underlying pointers differ", logger, obtained.lock(), prediction.lock());
    }
 
    template<test_mode Mode>
    static void test(equivalence_check_t, test_logger<Mode>& logger, const type& obtained, const type& prediction)
    {
      check(equivalence, "Underlying pointers differ", logger, obtained.lock(), prediction.lock());
    }
  };
 
 
  template<class R, class... Args>
  struct value_tester<std::function<R (Args...)>>
  {
    using type = std::function<R (Args...)>;
 
    template<test_mode Mode>
    static void test(weak_equivalence_check_t, test_logger<Mode>& logger, const type& obtained, const type& prediction)
    {
      const bool obtainedIsNull{obtained}, predictionIsNull{prediction};
 
      check(nullable_type_message(obtainedIsNull, predictionIsNull),
            logger,
            (obtainedIsNull && predictionIsNull) || (!obtainedIsNull && !predictionIsNull));
    }
  };
 
  template<class Clock, class Duration>
  struct value_tester<std::chrono::time_point<Clock, Duration>>
  {
    using type = std::chrono::time_point<Clock, Duration>;
 
    template<test_mode Mode, class Advisor>
    static void test(equality_check_t, test_logger<Mode>& logger, const type& obtained, const type& prediction, const tutor<Advisor>& advisor)
    {
      using ns = std::chrono::nanoseconds;
      check(equality,
            "Time since epoch",
            logger,
            std::chrono::duration_cast<ns>(obtained.time_since_epoch()),
            std::chrono::duration_cast<ns>(prediction.time_since_epoch()), advisor);
    }
  };
}