Add extra error messages regarding unused terms in IBLanguage.qwm

- Adds extra error messages to catch zero rows in qwm, which cause errors
- Adds extra testing to ensure the edge case is caught

Author: Ashvin-Ranjan

src/eff_conv/ib/language.py

@@ -51,6 +51,10 @@ def __init__(
             raise ValueError(
                 "All columns of conditional probability matrix must sum to 1"
             )
+        if (np.sum(qwm, axis=1) <= 0).any():
+            raise ValueError(
+                "All rows of conditional probability matrix must sum to a value greater than 0"
+            )
         if (qwm < 0).any():
             raise ValueError(
                 "No negative numbers are allowed in the probability matrix"

src/tests/test_ib.py

@@ -186,3 +186,5 @@ def test_ib_language_check(self):
             lang_negative_probability = IBLanguage(
                 self.simple_struct, np.array([[-1, 1], [2, 0]])
             )
+        with pytest.raises(ValueError):
+            lang_zero_row = IBLanguage(self.simple_struct, np.array([[1, 1], [0, 0]]))