fix: avoid None.strip() error in TCP mode by checking server_socket (#633)

### What problem were solved in this pull request?

Problem:
When `server_socket` parameter is `None` (which is valid when using TCP
port mode only), the code calls `server_socket.strip()` which raises an
`AttributeError` because `None` has no `strip()` method. This prevents
the test framework from initializing properly when Unix socket is not
configured.

### What is changed and how it works?

Modified all occurrences of `server_socket.strip()` to
`server_socket.strip() if server_socket else ''` in the following test
files:

1. `test/integration_test/miniob/miniob_client.py` - Line 36
2. `test/integration_test/miniob/miniob_server.py` - Line 57
3. `test/integration_test/miniob_test_util.py` - Lines 129 and 391
4. `test/case/miniob_test.py` - Lines 113 and 277

This change ensures that when `server_socket` is `None`, it is safely
converted to an empty string, allowing the code to fall back to TCP port
mode. The existing logic already handles empty strings correctly by
checking `if len(self.__server_socket) > 0` before attempting to use
Unix socket.

### Other information

This is a minimal fix that improves the robustness of the test framework
by handling the case where Unix socket is not configured.

Author: Gris333

test/case/miniob_test.py

@@ -110,7 +110,7 @@ def __init__(self, base_dir: str, data_dir: str, config_file: str, server_port:
     self.__check_config(config_file)
     self.__config = config_file
     self.__server_port = server_port
-    self.__server_socket = server_socket.strip()
+    self.__server_socket = server_socket.strip() if server_socket else ''
 
     self.__process = None
 
@@ -274,7 +274,7 @@ def __init__(self, server_port: int, server_socket: str, time_limit:int = 10):
       raise(Exception("Invalid server port: " + str(server_port)))
 
     self.__server_port = server_port
-    self.__server_socket = server_socket.strip()
+    self.__server_socket = server_socket.strip() if server_socket else ''
     self.__socket = None
     self.__buffer_size = 8192
 

test/integration_test/miniob/miniob_client.py

@@ -33,7 +33,7 @@ def __init__(self, *,
             self.__logger = _logger
 
         self.__server_port = server_port
-        self.__server_socket = server_socket.strip()
+        self.__server_socket = server_socket.strip() if server_socket else ''
         self.__time_limit = time_limit
         self.__socket = None
         self.__buffer_size = 8192

test/integration_test/miniob/miniob_server.py

@@ -54,7 +54,7 @@ def __init__(self, *,
         self.__check_config(config_file)
         self.__config = config_file
         self.__server_port = server_port
-        self.__server_socket = server_socket.strip()
+        self.__server_socket = server_socket.strip() if server_socket else ''
 
         self.__process = None
         self.__core_path = core_path

test/integration_test/miniob_test_util.py

@@ -126,7 +126,7 @@ def __init__(self, *,
         self.__check_config(config_file)
         self.__config = config_file
         self.__server_port = server_port
-        self.__server_socket = server_socket.strip()
+        self.__server_socket = server_socket.strip() if server_socket else ''
 
         self.__process = None
         self.__core_path = core_path
@@ -388,7 +388,7 @@ def __init__(self, *,
             self.__logger:logging.Logger = _logger
 
         self.__server_port = server_port
-        self.__server_socket = server_socket.strip()
+        self.__server_socket = server_socket.strip() if server_socket else ''
         self.__socket = None
         self.__buffer_size = 8192