test: prime cache in invalidation tests; use is-None cache guard

Six of the suffixes_prefixes_titles tests passed against the unfixed
code because they read the property only once on a cold cache, so they
asserted "the union includes its source sets" rather than "the cache
stays consistent after a mutation." Prime the cache before mutating so
they actually exercise invalidation; verified they now fail (14 across
the dual-run fixture) against master's pre-fix config.

Change the property guard from `if not self._pst` to `if self._pst is
None` so a legitimately empty union caches instead of recomputing on
every access — and so "cached" means "computed," which is the state the
primed tests rely on.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: derek73

nameparser/config/__init__.py

@@ -281,7 +281,7 @@ def _invalidate_pst(self) -> None:
 
     @property
     def suffixes_prefixes_titles(self) -> Set[str]:
-        if not self._pst:
+        if self._pst is None:
             self._pst = self.prefixes | self.suffix_acronyms | self.suffix_not_acronyms | self.titles
         return self._pst
 

tests/test_constants.py

@@ -108,12 +108,14 @@ def test_add_constant_with_explicit_encoding(self) -> None:
     def test_suffixes_prefixes_titles_reflects_add_title(self) -> None:
         """suffixes_prefixes_titles must include titles added after construction."""
         c = Constants()
+        _ = c.suffixes_prefixes_titles  # prime the cache so invalidation is exercised
         c.titles.add('emerita')
         self.assertIn('emerita', c.suffixes_prefixes_titles)
 
     def test_suffixes_prefixes_titles_reflects_add_prefix(self) -> None:
         """suffixes_prefixes_titles must include prefixes added after construction."""
         c = Constants()
+        _ = c.suffixes_prefixes_titles  # prime the cache so invalidation is exercised
         c.prefixes.add('xpfx')
         self.assertIn('xpfx', c.suffixes_prefixes_titles)
 
@@ -136,12 +138,14 @@ def test_suffixes_prefixes_titles_reflects_remove_prefix(self) -> None:
     def test_suffixes_prefixes_titles_reflects_add_suffix_acronym(self) -> None:
         """suffixes_prefixes_titles must include suffix acronyms added after construction."""
         c = Constants()
+        _ = c.suffixes_prefixes_titles  # prime the cache so invalidation is exercised
         c.suffix_acronyms.add('xsfx')
         self.assertIn('xsfx', c.suffixes_prefixes_titles)
 
     def test_suffixes_prefixes_titles_reflects_add_suffix_not_acronym(self) -> None:
         """suffixes_prefixes_titles must include non-acronym suffixes added after construction."""
         c = Constants()
+        _ = c.suffixes_prefixes_titles  # prime the cache so invalidation is exercised
         c.suffix_not_acronyms.add('xsfx')
         self.assertIn('xsfx', c.suffixes_prefixes_titles)
 
@@ -155,11 +159,13 @@ def test_suffixes_prefixes_titles_reflects_add_after_initial_read(self) -> None:
     def test_is_rootname_consistent_with_is_title(self) -> None:
         """is_rootname must return False for words recognised by is_title."""
         hn = HumanName("", constants=None)
+        _ = hn.C.suffixes_prefixes_titles  # prime the cache so a stale entry would be observable
         hn.C.titles.add('emerita')
         self.assertFalse(hn.is_rootname('emerita'))
 
     def test_is_rootname_consistent_with_is_prefix(self) -> None:
         """is_rootname must return False for words recognised by is_prefix."""
         hn = HumanName("", constants=None)
+        _ = hn.C.suffixes_prefixes_titles  # prime the cache so a stale entry would be observable
         hn.C.prefixes.add('xpfx')
         self.assertFalse(hn.is_rootname('xpfx'))