diff --git a/casimport/__init__.py b/casimport/__init__.py
index b58be4c..34f0a17 100644
--- a/casimport/__init__.py
+++ b/casimport/__init__.py
@@ -176,6 +176,10 @@ class Test(unittest.TestCase):
 		# That a CASFinder
 		f = CASFinder()
 
+		# make sure that we can't import anything at first
+		with self.assertRaises(ImportError):
+			import cas.v1_f_2398472398
+
 		# when registering the fixtures directory
 		f.register(FileDirCAS(self.fixtures))