diff --git a/tests/test_regs.py b/tests/test_regs.py
index fae237c..16d65b2 100644
--- a/tests/test_regs.py
+++ b/tests/test_regs.py
@@ -21,10 +21,12 @@ class TestRead(unittest.TestCase):
     def test_write_direct(self):
         current = gen24_registers.OutWRte.getValue(fronius1)
         retval = gen24_registers.OutWRte.setValue(fronius1, current)
+        assert retval is not None
 
     def test_write_scaled(self):
         current = gen24_registers.scaledInWRte.getValue(fronius1)
         retval = gen24_registers.scaledInWRte.setValue(fronius1, current)
+        assert retval is not None
 
 if __name__ == '__main__':
     unittest.main()