fix: format TopicInfo expiration_time in UTC (hiero-ledger#1802)

Signed-off-by: Eugene Sim <jcseugene@gmail.com>

Author: EugeneSim

CHANGELOG.md

@@ -1,4 +1,4 @@
-# Changelog
+# Changelog
 
 All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org).
@@ -12,6 +12,7 @@ This changelog is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.
 - Added CodeRabbit review instructions and path mapping for the schedule module (`src/hiero_sdk_python/schedule/`) in `.coderabbit.yaml` (#1698)
 
 ### Src
+- Fix `TopicInfo.__str__()` to format `expiration_time` in UTC so unit tests pass in non-UTC environments. (#1800)
 - 
 
 ### Examples

src/hiero_sdk_python/consensus/topic_info.py

@@ -6,7 +6,7 @@
 optional fields, and providing a readable string representation of the
 topic state.
 """
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import List, Optional
 
 from hiero_sdk_python.crypto.public_key import PublicKey
@@ -138,9 +138,12 @@ def __str__(self) -> str:
         Returns:
             str: A nicely formatted string representation of the topic.
         """
-        exp_dt: Optional[datetime] = None
+        exp_dt: Optional[str] = None
         if self.expiration_time and hasattr(self.expiration_time, "seconds"):
-            exp_dt = datetime.fromtimestamp(self.expiration_time.seconds)
+            utc_dt = datetime.fromtimestamp(
+                self.expiration_time.seconds, tz=timezone.utc
+            )
+            exp_dt = utc_dt.strftime("%Y-%m-%d %H:%M:%S")
 
         running_hash_str: Optional[str] = f"0x{self.running_hash.hex()}" if self.running_hash else "None"