minor: revisit _possibly_invalidate_import_caches

src/_pytest/pytester.py

@@ -611,12 +611,10 @@ class Testdir(object):
     def _possibly_invalidate_import_caches(self):
         # invalidate caches if we can (py33 and above)
         try:
-            import importlib
+            from importlib import invalidate_caches
         except ImportError:
-            pass
-        else:
-            if hasattr(importlib, "invalidate_caches"):
-                importlib.invalidate_caches()
+            return
+        invalidate_caches()
 
     def mkdir(self, name):
         """Create a new (sub)directory."""