diff --git a/nachrichten-manager-server/src/test/java/de/ozgcloud/nachrichten/file/AttachmentFileServiceTest.java b/nachrichten-manager-server/src/test/java/de/ozgcloud/nachrichten/file/AttachmentFileServiceTest.java
index 86484bf46a739fee0462aacf51ace9b2317d74f4..972a5e900e991c1aea4c6ed229af59d107ca8988 100644
--- a/nachrichten-manager-server/src/test/java/de/ozgcloud/nachrichten/file/AttachmentFileServiceTest.java
+++ b/nachrichten-manager-server/src/test/java/de/ozgcloud/nachrichten/file/AttachmentFileServiceTest.java
@@ -540,9 +540,11 @@ class AttachmentFileServiceTest {
 
 		@Test
 		void shouldReturnInputStream() {
+			when(decoder.decode(anyString())).thenReturn(FILE_CONTENT.getBytes());
+
 			var result = service.toDecodedInputStream(FILE_CONTENT);
 
-			assertThat(result).isNotNull();
+			assertThat(result).hasBinaryContent(FILE_CONTENT.getBytes());
 		}
 	}
 }
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