First unit tests, misc fixes

src/Broker/Message.php

@@ -23,11 +23,11 @@ class Message
 
     public function __construct(
         array $topic,
-        ?string $type,
-        ?string $data,
-        ?bool $private,
-        ?string $id,
-        ?int $retry
+        ?string $data=null,
+        ?string $type=null,
+        ?bool $private=null,
+        ?string $id=null,
+        ?int $retry=null
     )
     {
         $this->topic = $topic;
@@ -60,7 +60,7 @@ class Message
             topic: (array)$data['topic'],
             type: $data['type']??null,
             data: $data['data']??null,
-            private: match ($data['private']??null) { "on" => true, null => null, default => false },
+            private: match ($data['private']??null) { "on" => true, true => true, null => null, default => false },
             id: $data['id']??null,
             retry: $data['retry']??null,
         );

src/Broker/SubscriberInterface.php

@@ -7,4 +7,6 @@ interface SubscriberInterface
     public function deliver(Message $message): void;
 
     public function isAuthorized(): bool;
+
+    public function getPayload(): ?array;
 }