Attempt to catch error where NaN is introduced.

src/stats/chi.rs

@@ -25,7 +25,8 @@ fn test_statistic<const N: usize, C: Categorical<N>>(table: &ContingencyTable<N,
         let observed_count = table.observed_by_index(i) as i64;
         let diff = observed_count - expected_count;
         let error = diff.pow(2) as f64;
-        let incremental_error = error / (expected_count as f64);
+        let incremental_error = error / (expected_count as f64).min(1.0);
+        debug_assert!(!incremental_error.is_nan(), "The error must never be NaN.");
         sum += incremental_error;
     }
     sum