add test for dt in arg and kwarg

bnavigator · bnavigator · commit 75f3aef754b2 · 2020-12-31T11:37:13.000+01:00
diff --git a/control/tests/xferfcn_test.py b/control/tests/xferfcn_test.py
@@ -101,6 +101,13 @@ def test_constructor_nodt(self):
         sys = TransferFunction(sysin)
         assert sys.dt is None
 
+    def test_constructor_double_dt(self):
+        """Test that providing dt as arg and kwarg prefers arg with warning"""
+        with pytest.warns(UserWarning, match="received multiple dt.*"
+                                             "using positional arg"):
+            sys = TransferFunction(1, [1, 2, 3], 0.1, dt=0.2)
+        assert sys.dt == 0.1
+
     def test_add_inconsistent_dimension(self):
         """Add two transfer function matrices of different sizes."""
         sys1 = TransferFunction([[[1., 2.]]], [[[4., 5.]]])
diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -218,7 +218,8 @@ def __init__(self, *args, **kwargs):
         elif len(args) == 3:
             # Discrete time transfer function
             if 'dt' in kwargs:
-                warn('received multiple dt arguments, using positional arg dt=%s'%dt)
+                warn('received multiple dt arguments, '
+                     'using positional arg dt=%s' % dt)
         elif len(args) == 1:
             # TODO: not sure this can ever happen since dt is always present
             try:
