fix: update KafkaMessageStub implementation

Author: ytvnr

src/test/java/test/stub/KafkaMessageRequestStub.java

@@ -44,4 +44,12 @@ public Completable onMessages(final FlowableTransformer<KafkaMessage, KafkaMessa
         this.transformer = transformer;
         return Completable.complete();
     }
+
+    @Override
+    public String compression() {
+        return "";
+    }
+
+    @Override
+    public void compression(String compressionType) {}
 }

src/test/java/test/stub/KafkaMessageResponseStub.java

@@ -44,4 +44,12 @@ public Completable onMessages(final FlowableTransformer<KafkaMessage, KafkaMessa
         this.transformer = transformer;
         return Completable.complete();
     }
+
+    @Override
+    public String compression() {
+        return "";
+    }
+
+    @Override
+    public void compression(String compressionType) {}
 }

src/test/java/test/stub/KafkaMessageStub.java

@@ -30,6 +30,7 @@
 public class KafkaMessageStub implements KafkaMessage {
 
     private final Map<String, Buffer> recordHeaders = new ConcurrentHashMap<>();
+    private Buffer key;
     private Buffer content;
 
     public KafkaMessageStub(String content) {
@@ -55,7 +56,19 @@ public KafkaMessage removeRecordHeader(String key) {
 
     @Override
     public Buffer key() {
-        return null;
+        return key;
+    }
+
+    @Override
+    public KafkaMessage key(Buffer buffer) {
+        this.key = buffer;
+        return this;
+    }
+
+    @Override
+    public KafkaMessage key(String s) {
+        this.key = Buffer.buffer(s);
+        return this;
     }
 
     @Override
@@ -78,6 +91,11 @@ public String topic() {
         return "";
     }
 
+    @Override
+    public int sizeInBytes() {
+        return 0;
+    }
+
     @Override
     public String id() {
         return "";