diff --git a/main.py b/main.py
index add86c1..2125c74 100644
--- a/main.py
+++ b/main.py
@@ -4,7 +4,7 @@
 from nacl.signing import SigningKey
 from nacl.encoding import HexEncoder
 
-from minichain import Transaction, Blockchain, Block, State, Mempool, P2PNetwork, mine_block
+from minichain import Transaction, Blockchain, Block, Mempool, P2PNetwork, mine_block
 
 
 logger = logging.getLogger(__name__)
diff --git a/minichain/chain.py b/minichain/chain.py
index 78ac73f..96523db 100644
--- a/minichain/chain.py
+++ b/minichain/chain.py
@@ -12,9 +12,9 @@ class Blockchain:
     Manages the blockchain, validates blocks, and commits state transitions.
     """
 
-    def __init__(self):
+    def __init__(self, state=None):
         self.chain = []
-        self.state = State()
+        self.state = state if state is not None else State()
         self._lock = threading.RLock()
         self._create_genesis_block()
 
diff --git a/minichain/p2p.py b/minichain/p2p.py
index aacbf49..8786b9f 100644
--- a/minichain/p2p.py
+++ b/minichain/p2p.py
@@ -19,7 +19,7 @@ class P2PNetwork:
         }
     """
 
-    def __init__(self, handler_callback=None):
+    def __init__(self, handler_callback=None) -> None:
         self._handler_callback = None
         if handler_callback is not None:
             self.register_handler(handler_callback)
@@ -44,7 +44,7 @@ async def stop(self):
                     if hasattr(self.pubsub, method_name):
                         shutdown_meth = getattr(self.pubsub, method_name)
                         break
-                
+
                 if shutdown_meth:
                     import asyncio
                     res = shutdown_meth()
@@ -83,6 +83,9 @@ async def handle_message(self, msg):
         """
         Callback when a p2p message is received.
         """
+        if not callable(self._handler_callback):
+            logger.debug("Network: No handler callback set, ignoring message")
+            return
 
         try:
             if not hasattr(msg, "data"):
diff --git a/minichain/transaction.py b/minichain/transaction.py
index cdf4d99..e039084 100644
--- a/minichain/transaction.py
+++ b/minichain/transaction.py
@@ -12,7 +12,7 @@ def __init__(self, sender, receiver, amount, nonce, data=None, signature=None, t
         self.amount = amount
         self.nonce = nonce
         self.data = data            # Preserve None (do NOT normalize to "")
-        self.timestamp = round(timestamp * 1000) if timestamp is not None else round(time.time() * 1000) # Integer milliseconds for determinism
+        self.timestamp = int(timestamp) if timestamp is not None else int(time.time() * 1000)
         self.signature = signature  # Hex str
 
     def to_dict(self):