update ContentSerialization test

postssystem.core/src/commonTest/kotlin/com/insanusmokrassar/postssystem/core/api/ContentSerialization.kt

@@ -7,12 +7,16 @@ import kotlin.test.Test
 import kotlin.test.assertEquals
 
 class ContentSerialization {
+    private val simpleTextTestEntries = 10
+    private val simpleSpecialTestEntries = 10
+
     @Test
     fun test_that_content_correctly_serializing_and_deserializing() {
-        val contents = listOf(
-            SimpleTextContent("Example"),
-            SimpleSpecialContent("Some internal id")
-        )
+        val contents = (0 until simpleTextTestEntries).map {
+            SimpleTextContent("Example$it")
+        } + (0 until simpleSpecialTestEntries).map {
+            SimpleSpecialContent("$it")
+        }
 
         val registeredContentFakes = contents.map { content ->
             RegisteredContent(