chore(protocols): drop the unused PAT_MAC_ADDR from ospf.py (#1844)

pcapkit/protocols/application/ospf.py

@@ -60,7 +60,6 @@
 
 """
 import ipaddress
-import re
 from typing import TYPE_CHECKING, cast
 
 from pcapkit.const.ospf.authentication import Authentication as Enum_Authentication
@@ -89,9 +88,6 @@
 
 __all__ = ['OSPF']
 
-# Ethernet address pattern
-PAT_MAC_ADDR = re.compile(rb'(?i)(?:[0-9a-f]{2}[:-]){5}[0-9a-f]{2}')
-
 
 class OSPF(Application[Data_OSPF, Schema_OSPF],
            schema=Schema_OSPF, data=Data_OSPF):

tests/protocols/application/test_ospf_dead_pattern_1844_unit.py

@@ -0,0 +1,58 @@
+# -*- coding: utf-8 -*-
+"""The unused Ethernet-address pattern in the OSPF module.
+
+GitHub issue #1844. :mod:`pcapkit.protocols.application.ospf` defined a
+``PAT_MAC_ADDR`` that nothing read, a leftover that came along when OSPF moved
+to the application layer in #1031, and it imported :mod:`re` only to compile
+it. The constant and the import are gone. This pins that the constant stays
+gone and that the module does not import :mod:`re` without using it. The
+copies of the pattern in the Ethernet, ARP and PCAP-NG modules have readers
+and are untouched.
+
+"""
+from __future__ import annotations
+
+import ast
+import importlib.util
+import unittest
+
+from tests._support import reimport_once_per_class
+
+RUNTIME_DEPS = ('tbtrim', 'aenum', 'chardet', 'dictdumper')
+HAS_RUNTIME = all(importlib.util.find_spec(name) is not None for name in RUNTIME_DEPS)
+
+
+@unittest.skipUnless(HAS_RUNTIME, 'runtime dependencies not installed')
+class OSPFDeadPatternUnitTests(unittest.TestCase):
+    def setUp(self) -> None:
+        reimport_once_per_class(self)
+
+    def test_pat_mac_addr_is_gone(self) -> None:
+        from pcapkit.protocols.application import ospf
+
+        self.assertFalse(hasattr(ospf, 'PAT_MAC_ADDR'))
+
+    def test_re_is_not_imported_unused(self) -> None:
+        # Read the source of the module actually imported, so the check runs
+        # against the tree under test. ``re`` may come back if something uses
+        # it; what must not return is the import with no reader.
+        from pcapkit.protocols.application import ospf
+
+        with open(ospf.__file__, encoding='utf-8') as file:
+            tree = ast.parse(file.read())
+
+        imports_re = any(
+            alias.name == 're' and alias.asname is None
+            for node in tree.body if isinstance(node, ast.Import)
+            for alias in node.names
+        )
+        reads_re = any(
+            isinstance(node, ast.Name) and node.id == 're'
+            for node in ast.walk(tree)
+        )
+        self.assertFalse(imports_re and not reads_re,
+                         f'{ospf.__file__} imports re but never uses it')
+
+
+if __name__ == '__main__':
+    unittest.main()