Eliminate len() usage in tests

Author: uranusjr

src/pip/_internal/resolution/resolvelib/found_candidates.py

@@ -83,13 +83,12 @@ def __iter__(self):
             candidates = _insert_installed(self._installed, self._get_others())
         return _deduplicated_by_version(candidates)
 
-    @lru_cache(maxsize=1)
     def __len__(self):
         # type: () -> int
-        # Implement to satisfy the ABC check and used in tests. This is not
-        # needed by the resolver, and should not be used by the provider either
-        # (for performance reasons).
-        return sum(1 for _ in self)
+        # Implemented to satisfy the ABC check. This is not needed by the
+        # resolver, and should not be used by the provider either (for
+        # performance reasons).
+        raise NotImplementedError("don't do this")
 
     @lru_cache(maxsize=1)
     def __bool__(self):

tests/unit/resolution_resolvelib/test_requirement.py

@@ -61,7 +61,7 @@ def test_new_resolver_correct_number_of_matches(test_cases, factory):
         matches = factory.find_candidates(
             [req], Constraint.empty(), prefers_installed=False,
         )
-        assert len(list(matches)) == match_count
+        assert sum(1 for _ in matches) == match_count
 
 
 def test_new_resolver_candidates_match_requirement(test_cases, factory):