Update test_vasp_xml.py

Signed-off-by: Han Wang <92130845+wanghan-iapcm@users.noreply.github.com>

Author: wanghan-iapcm

tests/test_vasp_xml.py

@@ -27,7 +27,7 @@ def setUp(self):
         self.system_1.from_vasp_xml("poscars/vasprun.h2o.md.conv.xml")
         self.system_2 = dpdata.LabeledSystem()
         self.system_2.from_vasp_xml("poscars/vasprun.h2o.md.xml")
-        # check if frames 1:2 match
+        # check if frames 1:3 match
         self.system_2 = self.system_2[1:]
         self.places = 6