chore: added check fo the nodes

Signed-off-by: Manish Dait <daitmanish88@gmail.com>

Author: manishdait

src/hiero_sdk_python/client/client.py

@@ -166,6 +166,17 @@ def for_network(cls, network_map: dict[str, AccountId], network_name: str | None
         Returns:
             Client: A Client instance configured with the custom network.
         """
+        if not network_map:
+            raise ValueError("network_map cannot be empty")
+
+        first_node = next(iter(network_map.values()))
+        shard = first_node.shard
+        realm = first_node.realm
+
+        for account_id in network_map.values():
+            if shard != account_id.shard or realm != account_id.realm:
+                raise ValueError("network is not valid, all nodes must be in the same shard and realm")
+
         nodes = [_Node(account_id, address, None) for address, account_id in network_map.items()]
         return cls(Network(network=network_name, nodes=nodes))
 

tests/unit/client_test.py

@@ -579,3 +579,28 @@ def test_for_network_with_non_hosted_network_not_downgrade_tls(network):
     assert str(node._address) == "127.0.0.1:50212"
     assert node._address._is_transport_security() is True
     assert client.network.is_transport_security() is False  # Non hosted network.
+
+
+def test_for_network_with_empty_map_raises_error():
+    """Test that for_network raises ValueError when map is empty."""
+    with pytest.raises(ValueError, match="network_map cannot be empty"):
+        Client.for_network({})
+
+
+@pytest.mark.parametrize(
+    "invalid_map, error_msg",
+    [
+        (
+            {"127.0.0.1:50211": AccountId(0, 0, 3), "127.0.0.1:50212": AccountId(1, 0, 4)},
+            "network is not valid, all nodes must be in the same shard and realm",
+        ),
+        (
+            {"127.0.0.1:50211": AccountId(0, 0, 3), "127.0.0.1:50212": AccountId(0, 1, 4)},
+            "network is not valid, all nodes must be in the same shard and realm",
+        ),
+    ],
+)
+def test_for_network_invalid_shard_realm_raises_error(invalid_map, error_msg):
+    """Test that for_network catches mismatched shards or realms."""
+    with pytest.raises(ValueError, match=error_msg):
+        Client.for_network(invalid_map)