[#380] docs: add missing test case for malformed json

(cherry picked from commit a14f3df)

Author: MateuszNaKodach

kotlin/src/main/kotlin/org/axonframework/extensions/kotlin/serialization/AxonSerializers.kt

@@ -74,7 +74,7 @@ val replayTokenContextSerializer = String.serializer().nullable
 
 /**
  * Module defining serializers for Axon Framework's core event handling and messaging components.
- * This module includes serializers for TrackingTokens, ScheduleTokens, and ResponseTypes, enabling
+ * This module includes serializers for TrackingTokens, ScheduleTokens, ResponseTypes and MetaData enabling
  * seamless integration with Axon-based applications.
  */
 val AxonSerializersModule = SerializersModule {

kotlin/src/main/kotlin/org/axonframework/extensions/kotlin/serialization/MetaDataSerializer.kt

@@ -10,7 +10,6 @@ import kotlinx.serialization.encoding.Encoder
 import kotlinx.serialization.json.*
 import org.axonframework.messaging.MetaData
 import java.time.Instant
-import java.util.Date
 import java.util.UUID
 
 /**
@@ -23,14 +22,14 @@ import java.util.UUID
  * ### Supported value types
  * Each entry in the MetaData map must conform to one of the following:
  * - Primitives: [String], [Int], [Long], [Float], [Double], [Boolean]
- * - Complex types: [UUID], [Instant], [Date]
+ * - Complex types: [UUID], [Instant]
  * - Collections: [Collection], [List], [Set]
  * - Arrays: [Array]
  * - Nested Maps: [Map] with keys convertible to [String]
  *
  * ### Limitations
  * - Custom types that do not fall into the above categories will throw a [SerializationException]
- * - Deserialized non-primitive types (like [UUID], [Instant], [Date]) are restored as [String], not their original types
+ * - Deserialized non-primitive types (like [UUID], [Instant]) are restored as [String], not their original types
  *
  * This serializer guarantees structural integrity of nested metadata (e.g. map within list within map), while remaining format-agnostic.
  *
@@ -67,7 +66,6 @@ object MetaDataSerializer : KSerializer<MetaData> {
         is Float -> JsonPrimitive(value)
         is Double -> JsonPrimitive(value)
         is UUID -> JsonPrimitive(value.toString())
-        is Date -> JsonPrimitive(value.toString())
         is Instant -> JsonPrimitive(value.toString())
         is Map<*, *> -> JsonObject(value.entries.associate { (k, v) -> k.toString() to toJsonElement(v) })
         is Collection<*> -> JsonArray(value.map { toJsonElement(it) })

kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/MetaDataSerializerTest.kt

@@ -7,6 +7,8 @@ import org.axonframework.extensions.kotlin.serialization.AxonSerializersModule
 import org.axonframework.extensions.kotlin.serialization.KotlinSerializer
 import org.axonframework.messaging.MetaData
 import org.axonframework.serialization.SerializationException
+import org.axonframework.serialization.SimpleSerializedObject
+import org.axonframework.serialization.SimpleSerializedType
 import org.junit.jupiter.api.Assertions.*
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertThrows
@@ -229,4 +231,16 @@ class MetaDataSerializerTest {
         }
     }
 
-}
+    @Test
+    fun `should throw exception when deserializing malformed JSON`() {
+        val serializedType = SimpleSerializedType(MetaData::class.java.name, null)
+
+        val syntaxErrorJson = """{"key": value}"""  // missing quotes around value
+        val syntaxErrorObject = SimpleSerializedObject(syntaxErrorJson, String::class.java, serializedType)
+
+        assertThrows<SerializationException> {
+            jsonSerializer.deserialize<String, MetaData>(syntaxErrorObject)
+        }
+    }
+
+}