diff --git a/python/obitools3/unit_tests.py b/python/obitools3/unit_tests.py
index ac9795d..91134ca 100644
--- a/python/obitools3/unit_tests.py
+++ b/python/obitools3/unit_tests.py
@@ -47,7 +47,7 @@ def elements_names():
     names = ""
     for i in range(NB_ELEMENTS_PER_LINE):
         names = names + str(i) + ";" 
-    return names
+    return names[:-1]
 
 
 def random_obivalue(data_type):
@@ -82,12 +82,14 @@ class OBIDMS_Column_TestCase(unittest.TestCase):
         i=0
         for i in range(clone.get_nb_lines_used()) :
             assert clone[i] == self.col[i], "Different value in original column and cloned column"
+            assert clone[i] is not None, "None value"
         clone.close()
     def test_OBIDMS_column_set_and_get(self):
         for i in range(LINE_COUNT_FOR_TEST_COLUMN):
             v = random_obivalue(self.data_type_str)
             self.col[i] = v
             assert self.col[i] == v, "Different value than the set value"
+            assert self.col[i] is not None, "None value"
 
 
 class OBIDMS_Column_multiple_elements_TestCase(OBIDMS_Column_TestCase):
@@ -103,6 +105,7 @@ class OBIDMS_Column_multiple_elements_TestCase(OBIDMS_Column_TestCase):
         for i in range(SMALLER_LINE_COUNT_FOR_TEST_COLUMN):
             for e in range(NB_ELEMENTS_PER_LINE) :
                 assert clone.get_item(i, self.elts_names[e]) == self.col.get_item(i, self.elts_names[e]), "Different value in original column and cloned column"
+                assert clone.get_item(i, self.elts_names[e]) is not None, "None value"
         clone.close()
     def test_OBIDMS_column_set_and_get(self):
         for i in range(SMALLER_LINE_COUNT_FOR_TEST_COLUMN):
@@ -110,7 +113,7 @@ class OBIDMS_Column_multiple_elements_TestCase(OBIDMS_Column_TestCase):
                 v = random_obivalue(self.data_type_str)
                 self.col.set_item(i, self.elts_names[e], v)
                 assert self.col.get_item(i, self.elts_names[e]) == v, "Different value than the set value"
-
+                assert self.col.get_item(i, self.elts_names[e]) is not None, "None value"
 
 
 class OBIDMS_Column_OBI_INT_TestCase(OBIDMS_Column_TestCase):