diff --git a/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerCborTest.kt b/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerCborTest.kt
index 6f84578..7390dcb 100644
--- a/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerCborTest.kt
+++ b/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerCborTest.kt
@@ -5,12 +5,10 @@ import kotlinx.serialization.cbor.Cbor
 import org.axonframework.extensions.kotlin.serialization.KotlinSerializer
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
-import java.util.HexFormat
 
 class KotlinSerializerCborTest {
     @OptIn(ExperimentalSerializationApi::class)
     private val sut = KotlinSerializer(Cbor)
-    private val format = HexFormat.of()
 
     @Test
     fun testStandardList() {
@@ -21,7 +19,7 @@ class KotlinSerializerCborTest {
         val actual = sut.serialize(items, ByteArray::class.java)
         val expected = "9fbf646e616d65616163666f6f01ffbf646e616d65616263666f6f02ffff"
         assertEquals("List:org.axonframework.extensions.kotlin.serializer.TypeOne", actual.type.name)
-        assertEquals(expected, format.formatHex(actual.data))
+        assertEquals(expected, actual.data.toHex())
     }
 
     @Test
@@ -35,6 +33,6 @@ class KotlinSerializerCborTest {
         val actual = sut.serialize(items, ByteArray::class.java)
         val expected = "9f9f636f6e65bf646e616d65616163666f6f01ffff9f636f6e65bf646e616d65616263666f6f02ffff9f6374776fbf646e616d656163636261729f0304ffffff9f636f6e65bf646e616d65616463666f6f05ffffff"
         assertEquals("List:org.axonframework.extensions.kotlin.serializer.SuperType", actual.type.name)
-        assertEquals(expected, format.formatHex(actual.data))
+        assertEquals(expected, actual.data.toHex())
     }
 }
diff --git a/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerProtobufTest.kt b/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerProtobufTest.kt
index 275b688..a72d0b0 100644
--- a/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerProtobufTest.kt
+++ b/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/KotlinSerializerProtobufTest.kt
@@ -5,12 +5,10 @@ import kotlinx.serialization.protobuf.ProtoBuf
 import org.axonframework.extensions.kotlin.serialization.KotlinSerializer
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
-import java.util.HexFormat
 
 class KotlinSerializerProtobufTest {
     @OptIn(ExperimentalSerializationApi::class)
     private val sut = KotlinSerializer(ProtoBuf)
-    private val format = HexFormat.of()
 
     @Test
     fun testStandardList() {
@@ -21,7 +19,7 @@ class KotlinSerializerProtobufTest {
         val actual = sut.serialize(items, ByteArray::class.java)
         val expected = "02050a01611001050a01621002"
         assertEquals("List:org.axonframework.extensions.kotlin.serializer.TypeOne", actual.type.name)
-        assertEquals(expected, format.formatHex(actual.data))
+        assertEquals(expected, actual.data.toHex())
     }
 
     @Test
@@ -35,6 +33,6 @@ class KotlinSerializerProtobufTest {
         val actual = sut.serialize(items, ByteArray::class.java)
         val expected = "040c0a036f6e6512050a016110010c0a036f6e6512050a016210020e0a0374776f12070a0163100310040c0a036f6e6512050a01641005"
         assertEquals("List:org.axonframework.extensions.kotlin.serializer.SuperType", actual.type.name)
-        assertEquals(expected, format.formatHex(actual.data))
+        assertEquals(expected, actual.data.toHex())
     }
 }
diff --git a/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/hexExtensions.kt b/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/hexExtensions.kt
new file mode 100644
index 0000000..862b99c
--- /dev/null
+++ b/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/hexExtensions.kt
@@ -0,0 +1,5 @@
+package org.axonframework.extensions.kotlin.serializer
+
+// copied from https://www.baeldung.com/kotlin/byte-arrays-to-hex-strings#1-formatter
+fun ByteArray.toHex(): String =
+    joinToString("") { eachByte -> "%02x".format(eachByte) }
\ No newline at end of file
diff --git a/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/TestTypes.kt b/kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/testTypes.kt
similarity index 100%
rename from kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/TestTypes.kt
rename to kotlin/src/test/kotlin/org/axonframework/extensions/kotlin/serializer/testTypes.kt