use 'pass' in placeholder func

tests/test_dataset.py

@@ -67,7 +67,7 @@ class Simple1001TestCase(unittest.TestCase):
         self.nHeader    = 41
 
     def tearDown(self):
-        a = 1
+        pass
 
     def testOpen(self):
         ict      = icartt.Dataset(self.fn, loadData=False)