diff --git a/src/test/java/sirius/biz/storage/s3/ObjectStoresSpec.groovy b/src/test/java/sirius/biz/storage/s3/ObjectStoresSpec.groovy
deleted file mode 100644
index cc685a3ab..000000000
--- a/src/test/java/sirius/biz/storage/s3/ObjectStoresSpec.groovy
+++ /dev/null
@@ -1,101 +0,0 @@
-/*
- * Made with all the love in the world
- * by scireum in Remshalden, Germany
- *
- * Copyright by scireum GmbH
- * http://www.scireum.de - info@scireum.de
- */
-
-package sirius.biz.storage.s3
-
-import sirius.kernel.BaseSpecification
-import sirius.kernel.commons.Files
-import sirius.kernel.commons.Streams
-import sirius.kernel.commons.Tuple
-import sirius.kernel.di.std.Part
-
-import java.nio.charset.StandardCharsets
-
-class ObjectStoresSpec extends BaseSpecification {
-
-    @Part
-    private static ObjectStores stores
-
-    def "createBucketWorks"() {
-        File download
-        when:
-        File file = File.createTempFile("test", "")
-        FileOutputStream fout = new FileOutputStream(file)
-        for (int i = 0; i < 10024; i++) {
-            fout.write("This is a test.".getBytes(StandardCharsets.UTF_8))
-        }
-        fout.close()
-        and:
-        stores.store().upload(stores.store().getBucketName("test"), "test", file, null)
-        and:
-        download = stores.store().download(stores.store().getBucketName("test"), "test")
-        and:
-        def expectedContents = com.google.common.io.Files.toString(file, StandardCharsets.UTF_8)
-        def downloadedContents = com.google.common.io.Files.toString(download, StandardCharsets.UTF_8)
-        then:
-        expectedContents == downloadedContents
-        cleanup:
-        Files.delete(file)
-        Files.delete(download)
-    }
-
-    def "PUT and GET works"() {
-        File download
-        when:
-        File file = File.createTempFile("test", "")
-        FileOutputStream fout = new FileOutputStream(file)
-        for (int i = 0; i < 10024; i++) {
-            fout.write("This is a test.".getBytes(StandardCharsets.UTF_8))
-        }
-        fout.close()
-        and:
-        stores.store().upload(stores.store().getBucketName("test"), "test", file, null)
-        and:
-        download = stores.store().download(stores.store().getBucketName("test"), "test")
-        and:
-        URLConnection c = new URL(stores.store().
-                objectUrl(stores.store().getBucketName("test"), "test")).openConnection()
-        and:
-        def expectedContents = com.google.common.io.Files.toString(file, StandardCharsets.UTF_8)
-        def downloadedContents = com.google.common.io.Files.toString(download, StandardCharsets.UTF_8)
-        def downloadedData = new String(Streams.toByteArray(c.getInputStream()), StandardCharsets.UTF_8)
-        then:
-        expectedContents == downloadedData
-        and:
-        expectedContents == downloadedContents
-        cleanup:
-        Files.delete(file)
-        Files.delete((File) download)
-    }
-
-    def "ensureBucketExists"() {
-        when:
-        stores.store().ensureBucketExists(stores.store().getBucketName("exists"))
-        then:
-        stores.store().doesBucketExist(stores.store().getBucketName("exists"))
-        stores.bucketCache.get(Tuple.create(stores.store().name,
-                stores.store().getBucketName("exists").getName()))
-        !stores.store().doesBucketExist(stores.store().getBucketName("not-exists"))
-        stores.bucketCache.get(Tuple.create(stores.store().name,
-                stores.store().getBucketName("not-exists").getName())) == null
-    }
-
-    def "deleteBucket"() {
-        when:
-        stores.store().ensureBucketExists(stores.store().getBucketName("deleted"))
-        then:
-        stores.store().doesBucketExist(stores.store().getBucketName("deleted"))
-        when:
-        stores.store().deleteBucket(stores.store().getBucketName("deleted"))
-        then:
-        !stores.store().doesBucketExist(stores.store().getBucketName("deleted"))
-        stores.bucketCache.get(Tuple.create(stores.store().name,
-                stores.store().getBucketName("deleted").getName())) == null
-    }
-
-}
diff --git a/src/test/kotlin/sirius/biz/storage/s3/ObjectStoresTest.kt b/src/test/kotlin/sirius/biz/storage/s3/ObjectStoresTest.kt
new file mode 100644
index 000000000..4fb8b7c7b
--- /dev/null
+++ b/src/test/kotlin/sirius/biz/storage/s3/ObjectStoresTest.kt
@@ -0,0 +1,114 @@
+/*
+ * Made with all the love in the world
+ * by scireum in Remshalden, Germany
+ *
+ * Copyright by scireum GmbH
+ * http://www.scireum.de - info@scireum.de
+ */
+
+package sirius.biz.storage.s3
+
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.extension.ExtendWith
+import sirius.kernel.SiriusExtension
+import sirius.kernel.commons.Files
+import sirius.kernel.commons.Tuple
+import sirius.kernel.di.std.Part
+import java.io.File
+import java.io.FileOutputStream
+import java.net.URL
+import java.nio.file.Files as files_
+import java.nio.charset.StandardCharsets
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+/**
+ * Tests the [ObjectStores].
+ */
+@ExtendWith(SiriusExtension::class)
+class ObjectStoresTest {
+
+    @Test
+    fun `create bucket works`() {
+        val file = File.createTempFile("test", "")
+        val fout = FileOutputStream(file)
+        repeat(10024) {
+            fout.write("This is a test.".toByteArray(StandardCharsets.UTF_8))
+        }
+        fout.close()
+        stores.store().upload(stores.store().getBucketName("test"), "test", file, null)
+        val download = stores.store().download(stores.store().getBucketName("test"), "test")
+        val expectedContents = files_.readString(file.toPath(), StandardCharsets.UTF_8)
+        val downloadedContents = files_.readString(download.toPath(), StandardCharsets.UTF_8)
+        assertEquals(expectedContents, downloadedContents)
+        Files.delete(file)
+        Files.delete(download)
+    }
+
+    @Test
+    fun `PUT and GET works`() {
+        val file = File.createTempFile("test", "")
+        val fout = FileOutputStream(file)
+        repeat(10024) {
+            fout.write("This is a test.".toByteArray(StandardCharsets.UTF_8))
+        }
+        fout.close()
+        stores.store().upload(stores.store().getBucketName("test"), "test", file, null)
+        val download = stores.store().download(stores.store().getBucketName("test"), "test")
+        val c = URL(
+            stores.store().objectUrl(stores.store().getBucketName("test"), "test")
+        ).openConnection()
+
+        val expectedContents = files_.readString(file.toPath(), StandardCharsets.UTF_8)
+        val downloadedContents = files_.readString(download.toPath(), StandardCharsets.UTF_8)
+        val downloadedData = String(c.getInputStream().readAllBytes(), StandardCharsets.UTF_8)
+
+        assertEquals(expectedContents, downloadedData)
+        assertEquals(expectedContents, downloadedContents)
+        Files.delete(file)
+        Files.delete(download)
+    }
+
+    @Test
+    fun `ensure bucket exists`() {
+        stores.store().ensureBucketExists(stores.store().getBucketName("exists"))
+        stores.store().doesBucketExist(stores.store().getBucketName("exists"))
+        stores.bucketCache.get(
+            Tuple.create(
+                stores.store().name,
+                stores.store().getBucketName("exists").getName()
+            )
+        )
+        !stores.store().doesBucketExist(stores.store().getBucketName("not-exists"))
+        assertEquals(
+            null, stores.bucketCache.get(
+                Tuple.create(
+                    stores.store().name,
+                    stores.store().getBucketName("not-exists").getName()
+                )
+            )
+        )
+    }
+
+    @Test
+    fun `delete Bucket works`() {
+        stores.store().ensureBucketExists(stores.store().getBucketName("deleted"))
+        stores.store().doesBucketExist(stores.store().getBucketName("deleted"))
+        stores.store().deleteBucket(stores.store().getBucketName("deleted"))
+        assertFalse { stores.store().doesBucketExist(stores.store().getBucketName("deleted")) }
+        assertEquals(
+            null, stores.bucketCache.get(
+                Tuple.create(
+                    stores.store().name,
+                    stores.store().getBucketName("deleted").getName()
+                )
+            )
+        )
+    }
+
+    companion object {
+        @Part
+        @JvmStatic
+        private lateinit var stores: ObjectStores
+
+    }
+}