BUG: signal: correlation_lags, fail with meaningful error message if the mode is unknown (scipy#21808)

Author: matteobachetti

scipy/signal/_signaltools.py

@@ -405,6 +405,8 @@ def correlation_lags(in1_len, in2_len, mode='full'):
             lags = np.arange(lag_bound + 1)
         else:
             lags = np.arange(lag_bound, 1)
+    else:
+        raise ValueError(f"Mode {mode} is invalid")
     return lags
 
 

scipy/signal/tests/test_signaltools.py

@@ -2135,6 +2135,11 @@ def test_correlation_lags(mode, behind, input_size):
     assert_equal(lags.shape, correlation.shape)
 
 
+def test_correlation_lags_invalid_mode():
+    with pytest.raises(ValueError, match="Mode asdfgh is invalid"):
+        correlation_lags(100, 100, mode="asdfgh")
+
+
 @pytest.mark.parametrize('dt', [np.csingle, np.cdouble,
                                 pytest.param(np.clongdouble, marks=_pmf)])
 class TestCorrelateComplex: