attempt making vr image test usable without a data dir setup

yt/testing.py

@@ -958,6 +958,13 @@ def requires_file(req_file):
     return skipif(condition, reason=f"Missing required file {req_file}")
 
 
+def requires_file_v2(req_file):
+    condition = not os.path.exists(
+        os.path.join(ytcfg.get("yt", "test_data_dir"), req_file)
+    )
+    return skipif(condition, reason=f"Missing required file {req_file}")
+
+
 def disable_dataset_cache(func):
     @wraps(func)
     def newfunc(*args, **kwargs):

yt/visualization/volume_rendering/tests/test_mesh_render.py

@@ -5,7 +5,7 @@
 from yt.testing import (
     fake_hexahedral_ds,
     fake_tetrahedral_ds,
-    requires_file,
+    requires_file_v2 as requires_file,
     requires_module,
 )
 from yt.utilities.answer_testing.framework import data_dir_load, data_dir_load_v2