diff --git a/bladex/shaft.py b/bladex/shaft.py
index b25c6e6..fab87ae 100755
--- a/bladex/shaft.py
+++ b/bladex/shaft.py
@@ -13,6 +13,7 @@ class Shaft(object):
         stored shaft information.
     :cvar string filename: path (with the file extension) of a .stl or .iges file with 
         stored shaft information.
+    :raises Exception: if the extension in the filename is not in .stl or .iges formats.
     """
 
     def __init__(self, filename):
diff --git a/tests/test_shaft.py b/tests/test_shaft.py
index 48dda05..77d18cb 100755
--- a/tests/test_shaft.py
+++ b/tests/test_shaft.py
@@ -20,7 +20,8 @@ def test_generate_solid_02(self):
 
     def test_exception(self):
     	sh = Shaft("tests/test_datasets/parameters.prm")
-    	sh.generate_solid()
+    	with self.assertRaises(Exception):
+    		sh.generate_solid()
 
     def test_display_01(self):
         sh = Shaft("tests/test_datasets/shaft.iges")