docs(tests): tighten the protocols test prose from the post-sweep merges (#719)

tests/protocols/internet/test_ipv6_ext_unit.py

@@ -121,9 +121,9 @@ def test_overrun_warns_and_stops_instead_of_clipping(self) -> None:
 
     def test_index_raises_because_no_class_level_identity_exists(self) -> None:
         """The fallback has no class-level identity, so it keeps raising rather
-        than being handed a placeholder index. This is also the other half of
-        the #917 contract in :class:`IPv6ExtSharedBaseContractTests`, which
-        relies on this test rather than repeating it.
+        than being handed a placeholder index.
+        :class:`IPv6ExtSharedBaseContractTests` relies on this test for that
+        half of the #917 contract.
         """
         from pcapkit.protocols.internet.ipv6_ext import IPv6_Ext
         from pcapkit.utilities.exceptions import UnsupportedCall

tests/protocols/misc/test_pcapng_unit.py

@@ -3910,8 +3910,7 @@ class PCAPNGTruncatedFileTests(unittest.TestCase):
 
     #: The result of :meth:`_sweep`, computed by the first test that asks for it
     #: and shared by the other three: one extraction per octet of the sample is
-    #: the cost of this class, and every test reads the same result (GitHub
-    #: issue #1062).
+    #: this class's whole cost (GitHub issue #1062).
     _swept = None  # type: tuple[dict[int, int], dict[int, BaseException]] | None
 
     @classmethod

tests/protocols/schema/test_schema_metaclass_abc_cache_unit.py

@@ -52,10 +52,12 @@ class was reading and writing the same ``isinstance`` cache that
 
     def setUp(self) -> None:
         # Fresh :mod:`pcapkit` classes *and* a freshly reset
-        # :mod:`collections.abc` cache -- :func:`purge_modules` does both, and
-        # both matter: a stale positive cache entry left over from an earlier
-        # test in the same process would make the very first assertion below
-        # true for the wrong reason.
+        # :mod:`collections.abc` cache, for every test. Both matter: a stale
+        # positive cache entry left over from an earlier test in the same
+        # process would make the very first assertion below true for the wrong
+        # reason. :func:`reimport_once_per_class` resets the cache each time;
+        # the classes are fresh each time only because ``tearDown`` purges them
+        # before :func:`reimport_once_per_class` can keep them for the next test.
         reimport_once_per_class(self)
 
     def tearDown(self) -> None:

tests/protocols/test_dispatch_reachability_unit.py

@@ -191,11 +191,11 @@ def __index__(cls) -> 'Any':
             self.assertTrue(any(name.endswith('Unreachable') for name in names),
                             f'audit missed the injected gap; reported {names}')
         finally:
-            # ``__subclasses__`` holds a weak reference, but the class is only
-            # collected once nothing in this frame names it -- and, a class
-            # being a reference cycle of its own, once the cycle collector has
-            # run. Until then the next audit in the same import still sees it
-            # (GitHub issue #1065: no longer one import per test).
+            # ``__subclasses__`` holds a weak reference, but a class is a
+            # reference cycle of its own, so it is only collected once nothing
+            # in this frame names it *and* the cycle collector has run. Until
+            # then the next audit on the class's shared import still sees it
+            # (GitHub issue #1065).
             del Unreachable
             gc.collect()
 

tests/protocols/test_dispatch_registry_unit.py

@@ -94,9 +94,9 @@ class DispatchRegistryTests(unittest.TestCase):
     """One dispatch probe per entry across all seven ``__proto__`` registries."""
 
     #: The generator module, loaded once for the whole class. Loading it
-    #: imports :mod:`pcapkit`, so it must happen after :meth:`setUp` has purged
-    #: the previous test's copy -- hence a class attribute filled in
-    #: :meth:`setUpClass` rather than a module-level import.
+    #: imports :mod:`pcapkit`, so it must happen after the purge in
+    #: :meth:`setUpClass` -- hence a class attribute filled in there rather
+    #: than a module-level import.
     dispatch = None  # type: Any
 
     @classmethod

tests/protocols/test_option_roundtrip_unit.py

@@ -583,9 +583,9 @@ class OptionRoundTripTests(unittest.TestCase):
     """One construct -> parse -> construct cycle per registered code."""
 
     #: The generator module, loaded once for the whole class. Loading it imports
-    #: :mod:`pcapkit`, so it must happen after :meth:`setUp` has purged the
-    #: previous test's copy -- hence a class attribute filled in
-    #: :meth:`setUpClass` rather than a module-level import.
+    #: :mod:`pcapkit`, so it must happen after the purge in :meth:`setUpClass`
+    #: -- hence a class attribute filled in there rather than a module-level
+    #: import.
     options = None  # type: Any
 
     @classmethod