lm: predict() does not always return pd.Series

src/tlo/lm.py

@@ -456,6 +456,7 @@ def predict(
             # pop the boolean out of the series if we have a single row,
             # otherwise return the series
             if len(outcome) == 1 and squeeze_single_row_output:
+                assert isinstance(outcome.iloc[0], pd.Series)
                 return outcome.iloc[0]
             else:
                 return outcome