diff --git a/tests/generator/comp_sys.py b/tests/generator/comp_sys.py
index 8806ddb5e..db37ad843 100644
--- a/tests/generator/comp_sys.py
+++ b/tests/generator/comp_sys.py
@@ -86,6 +86,9 @@ def test_coord(self):
         tmp_cell = self.system_1.data["cells"]
         tmp_cell = np.reshape(tmp_cell, [-1, 3])
         tmp_cell_norm = np.reshape(np.linalg.norm(tmp_cell, axis=1), [-1, 3])
+        if np.max(np.abs(tmp_cell_norm)) < 1e-12:
+            # zero cell, no pbc case, set to [1., 1., 1.]
+            tmp_cell_norm = np.ones(tmp_cell_norm.shape)
         for ff in range(self.system_1.get_nframes()):
             for ii in range(sum(self.system_1.data["atom_numbs"])):
                 for jj in range(3):
@@ -103,12 +106,21 @@ class CompLabeledSys(CompSys):
     def test_energy(self):
         self.assertEqual(self.system_1.get_nframes(), self.system_2.get_nframes())
         for ff in range(self.system_1.get_nframes()):
-            self.assertAlmostEqual(
-                self.system_1.data["energies"][ff],
-                self.system_2.data["energies"][ff],
-                places=self.e_places,
-                msg="energies[%d] failed" % (ff),
-            )
+            if abs(self.system_2.data["energies"][ff]) < 1e-12:
+                self.assertAlmostEqual(
+                    self.system_1.data["energies"][ff],
+                    self.system_2.data["energies"][ff],
+                    places=self.e_places,
+                    msg="energies[%d] failed" % (ff),
+                )
+            else:
+                self.assertAlmostEqual(
+                    self.system_1.data["energies"][ff]
+                    / self.system_2.data["energies"][ff],
+                    1.0,
+                    places=self.e_places,
+                    msg="energies[%d] failed" % (ff),
+                )
 
     def test_force(self):
         self.assertEqual(self.system_1.get_nframes(), self.system_2.get_nframes())