refactored identifier, added tests and added primary_key_accessor and tests

test/core/CMakeLists.txt

@@ -5,6 +5,7 @@ list(APPEND CMAKE_MODULE_PATH ${catch2_SOURCE_DIR}/extras)
 add_executable(CoreTests
   ../backends/SchemaFixture.hpp
   logger/LoggerTest.cpp
+  object/ObjectCacheTest.cpp
   object/ObjectTest.cpp
   object/PrimaryKeyResolverTest.cpp
   object/RepositoryTest.cpp
@@ -14,13 +15,13 @@ add_executable(CoreTests
   utils/DependencyInjectionTest.cpp
   utils/FieldAttributeTest.cpp
   utils/IdentifierTest.cpp
+  utils/IsDatabasePrimitiveTest.cpp
   utils/MessageBusTest.cpp
+  utils/PrimaryKeyAccessorTest.cpp
   utils/ResultTest.cpp
   utils/StringTest.cpp
   utils/ThreadPoolTest.cpp
   utils/VersionTest.cpp
-  utils/IsDatabasePrimitiveTest.cpp
-  object/ObjectCacheTest.cpp
 )
 
 target_link_libraries(CoreTests matador-core Catch2::Catch2WithMain)