small bm25 test that makes sure terms are scaled

crates/core/src/ranking/bm25.rs

@@ -181,3 +181,28 @@ impl Bm25Weight {
  explanation
  }
 }
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[test]
+ fn test_bm25_idf_scaling() {
+ // assume the query is something like 'the end'
+ // 'the' appears in almost all docs (98)
+ // 'end' appears in a smalle subset (20)
+ let weight = MultiBm25Weight {
+ weights: vec![
+ Bm25Weight::for_one_term(98, 100, 1.0),
+ Bm25Weight::for_one_term(20, 100, 1.0),
+ ],
+ };
+
+ // if a document has high frequency of 'end'
+ // it should have a higher score than a document that
+ // has an almost equally high frequency of 'the'
+ let high_the = weight.score(vec![(0, 15), (0, 10)].into_iter());
+ let high_end = weight.score(vec![(0, 8), (0, 13)].into_iter());
+ assert!(high_end > high_the);
+ }
+}