[KPM] IdeaKotlinProjectModelSerializableTest compare by string representation

KT-51262
KT-51220

libraries/tools/kotlin-gradle-plugin-idea/src/main/kotlin/org/jetbrains/kotlin/gradle/kpm/KotlinExternalModelContainer.kt

@@ -25,6 +25,10 @@ abstract class KotlinExternalModelContainer internal constructor() : Serializabl
         override fun <T : Any> contains(key: KotlinExternalModelKey<T>): Boolean = false
         override fun <T : Any> get(key: KotlinExternalModelKey<T>): T? = null
     }
+
+    override fun toString(): String {
+        return "KotlinExternalModelContainer(${ids.joinToString("; ", "[", "]")}"
+    }
 }
 
 abstract class KotlinMutableExternalModelContainer internal constructor() : KotlinExternalModelContainer() {

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/kpm/idea/IdeaKotlinProjectModelSerializableTest.kt

@@ -21,7 +21,7 @@ import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.fail
 
-class KotlinIdeaProjectModelSerializableTest : AbstractKpmExtensionTest() {
+class IdeaKotlinProjectModelSerializableTest : AbstractKpmExtensionTest() {
 
     @Test
     fun `test - serialize and deserialize - empty project`() {
@@ -61,8 +61,8 @@ class KotlinIdeaProjectModelSerializableTest : AbstractKpmExtensionTest() {
         }
 
         assertEquals(
-            model, deserializedModel,
-            "Expected deserializedModel to match source model"
+            model.toString(), deserializedModel.toString(),
+            "Expected deserializedModel string representation to match source model"
         )
     }
 }