From 65f0b622e390edb39a6cfd8d614374314472a5a9 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Sat, 28 Dec 2019 17:22:06 +0100
Subject: new_type: add equality comparison tests

---
 CMakeLists.txt                             |   1 +
 include/newtype/new_type.hpp               |  10 +-
 test/include/equality_comparison_suite.hpp |  11 +++
 test/src/driver.cpp                        |   2 +
 test/src/equality_comparison_suite.cpp     | 145 +++++++++++++++++++++++++++++
 5 files changed, 166 insertions(+), 3 deletions(-)
 create mode 100644 test/include/equality_comparison_suite.hpp
 create mode 100644 test/src/equality_comparison_suite.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9977012..b78a58e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -51,6 +51,7 @@ if(BUILD_TESTING)
 
     "${PROJECT_SOURCE_DIR}/test/src/derivation_clause_suite.cpp"
     "${PROJECT_SOURCE_DIR}/test/src/conversion_suite.cpp"
+    "${PROJECT_SOURCE_DIR}/test/src/equality_comparison_suite.cpp"
     "${PROJECT_SOURCE_DIR}/test/src/new_type_constructor_suite.cpp"
     )
 
diff --git a/include/newtype/new_type.hpp b/include/newtype/new_type.hpp
index 67e29c3..c0fb8d3 100644
--- a/include/newtype/new_type.hpp
+++ b/include/newtype/new_type.hpp
@@ -134,7 +134,9 @@ namespace nt
    */
   template<typename BaseType, typename TagType, auto DerivationClause>
   auto constexpr operator==(new_type<BaseType, TagType, DerivationClause> const & lhs,
-                            new_type<BaseType, TagType, DerivationClause> const & rhs) noexcept(noexcept(lhs.decay() == rhs.decay())) -> bool
+                            new_type<BaseType, TagType, DerivationClause> const & rhs) noexcept(noexcept(std::declval<BaseType const &>() ==
+                                                                                                         std::declval<BaseType const &>()))
+      -> bool
   {
     return lhs.decay() == rhs.decay();
   }
@@ -144,9 +146,11 @@ namespace nt
    */
   template<typename BaseType, typename TagType, auto DerivationClause>
   auto constexpr operator!=(new_type<BaseType, TagType, DerivationClause> const & lhs,
-                            new_type<BaseType, TagType, DerivationClause> const & rhs) noexcept(noexcept(!(lhs == rhs))) -> bool
+                            new_type<BaseType, TagType, DerivationClause> const & rhs) noexcept(noexcept(std::declval<BaseType const &>() !=
+                                                                                                         std::declval<BaseType const &>()))
+      -> bool
   {
-    return !(lhs == rhs);
+    return lhs.decay() != rhs.decay();
   }
 
 }  // namespace nt
diff --git a/test/include/equality_comparison_suite.hpp b/test/include/equality_comparison_suite.hpp
new file mode 100644
index 0000000..80abbe7
--- /dev/null
+++ b/test/include/equality_comparison_suite.hpp
@@ -0,0 +1,11 @@
+#ifndef NEWTYPE_TEST_EQUALITY_COMPARISON_SUITE_HPP
+#define NEWTYPE_TEST_EQUALITY_COMPARISON_SUITE_HPP
+
+#include <cute/cute_suite.h>
+
+#include <string>
+#include <utility>
+
+auto equality_comparison_suite() -> std::pair<cute::suite, std::string>;
+
+#endif
\ No newline at end of file
diff --git a/test/src/driver.cpp b/test/src/driver.cpp
index 6c1ae7d..f6afe58 100644
--- a/test/src/driver.cpp
+++ b/test/src/driver.cpp
@@ -1,5 +1,6 @@
 #include "conversion_suite.hpp"
 #include "derivation_clause_suite.hpp"
+#include "equality_comparison_suite.hpp"
 #include "new_type_constructor_suite.hpp"
 
 #include <cute/cute.h>
@@ -51,6 +52,7 @@ int main(int argc, char ** argv)
       derivation_clause_suite(),
       new_type_constructor_suite(),
       conversion_suite(),
+      equality_comparison_suite(),
   };
 
   auto selectors = get_test_selectors(suites);
diff --git a/test/src/equality_comparison_suite.cpp b/test/src/equality_comparison_suite.cpp
new file mode 100644
index 0000000..64c7521
--- /dev/null
+++ b/test/src/equality_comparison_suite.cpp
@@ -0,0 +1,145 @@
+#include "equality_comparison_suite.hpp"
+
+#include "kawaii.hpp"
+#include "newtype/derivable.hpp"
+#include "newtype/deriving.hpp"
+#include "newtype/new_type.hpp"
+
+#include <cute/cute.h>
+
+#include <string>
+#include <type_traits>
+#include <utility>
+
+inline namespace basic_equality_comparsion_tests
+{
+
+  auto two_instances_of_the_same_new__type_with_the_same_value_compare_equal() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_1>;
+
+    auto constexpr lhs = type_alias{42};
+    auto constexpr rhs = type_alias{42};
+
+    ASSERT_EQUAL(lhs, rhs);
+  }
+
+  auto two_instances_of_the_same_new__type_with_the_same_value_do_not_compare_not_equal() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_1>;
+
+    auto constexpr lhs = type_alias{42};
+    auto constexpr rhs = type_alias{42};
+
+    ASSERT(!(lhs != rhs));
+  }
+
+  auto two_instances_of_the_same_new__type_with_differing_values_do_compare_not_equal() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_1>;
+
+    auto constexpr lhs = type_alias{42};
+    auto constexpr rhs = type_alias{43};
+
+    ASSERT_NOT_EQUAL_TO(lhs, rhs);
+  }
+
+  auto two_instances_of_the_same_new__type_with_differing_values_do_not_compare_equal() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_1>;
+
+    auto constexpr lhs = type_alias{42};
+    auto constexpr rhs = type_alias{43};
+
+    ASSERT(!(lhs == rhs));
+  }
+
+}  // namespace basic_equality_comparsion_tests
+
+inline namespace equality_comparsion_noexcept_tests
+{
+
+  auto equality_comparison_on_a_new__type_is_noexcept_if_the_base_type_is_noexcept_comparable() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_2>;
+    static_assert(noexcept(std::declval<int &>() == std::declval<int &>()), "Sanity Check");
+    ASSERT(noexcept(std::declval<type_alias &>() == std::declval<type_alias &>()));
+  }
+
+  auto equality_comparison_on_a_new__type_is_not_noexcept_if_the_base_type_is_not_noexcept_comparable() -> void
+  {
+    struct strange_type
+    {
+      auto constexpr operator==(strange_type const &) const noexcept(false) -> bool
+      {
+        return false;
+      }
+    };
+
+    using type_alias = nt::new_type<strange_type, struct eq_test_tag_3>;
+    static_assert(!noexcept(std::declval<strange_type &>() == std::declval<strange_type &>()), "Sanity Check");
+    ASSERT(!noexcept(std::declval<type_alias &>() == std::declval<type_alias &>()));
+  }
+
+  auto inequality_comparison_on_a_new__type_is_noexcept_if_the_base_type_is_noexcept_comparable() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_4>;
+    static_assert(noexcept(std::declval<int &>() != std::declval<int &>()), "Sanity Check");
+    ASSERT(noexcept(std::declval<type_alias &>() != std::declval<type_alias &>()));
+  }
+
+  auto inequality_comparison_on_a_new__type_is_not_noexcept_if_the_base_type_is_not_noexcept_comparable() -> void
+  {
+    struct strange_type
+    {
+      auto constexpr operator!=(strange_type const &) const noexcept(false) -> bool
+      {
+        return false;
+      }
+    };
+
+    using type_alias = nt::new_type<strange_type, struct eq_test_tag_5>;
+    static_assert(!noexcept(std::declval<strange_type &>() != std::declval<strange_type &>()), "Sanity Check");
+    ASSERT(!noexcept(std::declval<type_alias &>() != std::declval<type_alias &>()));
+  }
+
+}  // namespace equality_comparsion_noexcept_tests
+
+inline namespace equality_comparison_return_type_tests
+{
+
+  auto equality_comparsion_of_two_new__type_instances_returns_bool() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_6>;
+    ASSERT((std::is_same_v<bool, decltype(std::declval<type_alias &>() == std::declval<type_alias &>())>));
+  }
+
+  auto inequality_comparsion_of_two_new__type_instances_returns_bool() -> void
+  {
+    using type_alias = nt::new_type<int, struct eq_test_tag_7>;
+    ASSERT((std::is_same_v<bool, decltype(std::declval<type_alias &>() != std::declval<type_alias &>())>));
+  }
+
+}  // namespace equality_comparison_return_type_tests
+
+auto equality_comparison_suite() -> std::pair<cute::suite, std::string>
+{
+  return {{
+              // Basic Equality Comparison Tests
+              KAWAII(two_instances_of_the_same_new__type_with_the_same_value_compare_equal),
+              KAWAII(two_instances_of_the_same_new__type_with_the_same_value_do_not_compare_not_equal),
+              KAWAII(two_instances_of_the_same_new__type_with_differing_values_do_compare_not_equal),
+              KAWAII(two_instances_of_the_same_new__type_with_differing_values_do_not_compare_equal),
+
+              // Equality Comparison noexcept Tests
+              KAWAII(equality_comparison_on_a_new__type_is_noexcept_if_the_base_type_is_noexcept_comparable),
+              KAWAII(equality_comparison_on_a_new__type_is_not_noexcept_if_the_base_type_is_not_noexcept_comparable),
+              KAWAII(inequality_comparison_on_a_new__type_is_noexcept_if_the_base_type_is_noexcept_comparable),
+              KAWAII(inequality_comparison_on_a_new__type_is_not_noexcept_if_the_base_type_is_not_noexcept_comparable),
+
+              // Equality Comparison Return Type Tests
+              KAWAII(equality_comparsion_of_two_new__type_instances_returns_bool),
+              KAWAII(inequality_comparsion_of_two_new__type_instances_returns_bool),
+          },
+          "Equality Comparison Tests"};
+}
\ No newline at end of file
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