Fix grammar cache problems, because multiple grammars were potentially loaded

test/test_api/test_api.py

@@ -9,19 +9,20 @@ from pytest import raises
 from parso import cache
 
 from jedi import preload_module
-from jedi._compatibility import is_py3
 from jedi.plugins import typeshed
 
 
 def test_preload_modules():
     def check_loaded(*modules):
-        # +1 for None module (currently used)
-        grammar_cache = next(iter(cache.parser_cache.values()))
+        for grammar_cache in cache.parser_cache.values():
+            if None in grammar_cache:
+                break
         # Filter the typeshed parser cache.
         typeshed_cache_count = sum(
             1 for path in grammar_cache
             if path is not None and path.startswith(typeshed._TYPESHED_PATH)
         )
+        # +1 for None module (currently used)
         assert len(grammar_cache) - typeshed_cache_count == len(modules) + 1
         for i in modules:
             assert [i in k for k in grammar_cache.keys() if k is not None]