Force polymorphic serialization in serialization tests

This ensures type information is always embedded in the serialized form. The "unknown type" serializers depend on this. Currently unknown type serializers always embed type information, but this should not be a requirement. A functionally correct implementation should only embed it in the case of polymorphic serialization.

Author: Whathecode

carp.test/src/commonMain/kotlin/dk/cachet/carp/test/serialization/ConcreteTypesSerializationTest.kt

@@ -49,10 +49,13 @@ abstract class ConcreteTypesSerializationTest(
         for ( toSerialize in instancesToSerialize )
         {
             // Get serializer.
+            // Polymorphic serializer is used to ensure type information is always embedded,
+            // which some deserializers may depend upon.
             val type = toSerialize::class
+            val registration = polymorphicSerializers[ type ]
+            assertNotNull( registration, "No serializer registered for type '$type'" )
             @Suppress( "UNCHECKED_CAST" )
-            val serializer = polymorphicSerializers[ type ] as? KSerializer<Any>
-            assertNotNull( serializer, "No serializer registered for type '$type'" )
+            val serializer = PolymorphicSerializer( registration.baseKlass ) as KSerializer<Any>
 
             // Verify whether serializing and deserializing the instance results in the same object.
             val serialized = json.encodeToString( serializer, toSerialize )
@@ -67,12 +70,12 @@ abstract class ConcreteTypesSerializationTest(
  * Get a map which holds the [KSerializer] for each [KClass] registered for polymorphic serialization in [serialModule].
  */
 @ExperimentalSerializationApi
-fun getPolymorphicSerializers( serialModule: SerializersModule ): Map<KClass<*>, KSerializer<*>>
+fun getPolymorphicSerializers( serialModule: SerializersModule ): Map<KClass<*>, PolymorphicRegistration>
 {
     val collector =
         object : SerializersModuleCollector
         {
-            val serializers: MutableMap<KClass<*>, KSerializer<*>> = mutableMapOf()
+            val serializers: MutableMap<KClass<*>, PolymorphicRegistration> = mutableMapOf()
 
             override fun <T : Any> contextual(
                 kClass: KClass<T>,
@@ -85,7 +88,7 @@ fun getPolymorphicSerializers( serialModule: SerializersModule ): Map<KClass<*>,
                 actualSerializer: KSerializer<Sub>
             )
             {
-                serializers[ actualClass ] = actualSerializer
+                serializers[ actualClass ] = PolymorphicRegistration( baseClass, actualSerializer )
             }
 
             @Suppress( "REDUNDANT_PROJECTION", "KotlinRedundantDiagnosticSuppress" ) // Exact override needed.
@@ -109,3 +112,6 @@ fun getPolymorphicSerializers( serialModule: SerializersModule ): Map<KClass<*>,
     serialModule.dumpTo( collector )
     return collector.serializers
 }
+
+
+data class PolymorphicRegistration( val baseKlass: KClass<*>, val serializer: KSerializer<*> )