Fix sim_hashes_search filtering and add unit test

Author: itsibitzi

crates/geo_filters/src/diff_count/sim_hash.rs

@@ -104,12 +104,12 @@ impl<C: GeoConfig<Diff>> GeoDiffCount<'_, C> {
         expected_diff_size: usize,
     ) -> (impl Iterator<Item = SimHash> + '_, usize) {
         let range = self.sim_hash_range(expected_diff_size);
-        let sim_hash_iter = self.sim_hashes();
-        let min_matches = sim_hash_iter
+        let min_matches = range
             .len()
             .saturating_sub(expected_diff_size)
             .max(SIM_BUCKETS / 2);
-        let filtered_iter = sim_hash_iter
+        let filtered_iter = self
+            .sim_hashes()
             .skip_while(move |(bucket_id, _)| *bucket_id >= range.end)
             .take_while(move |(bucket_id, _)| *bucket_id >= range.start)
             .map(|(_, sim_hash)| sim_hash);
@@ -222,3 +222,28 @@ impl BitVec<'_> {
         None
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use rand::Rng as _;
+
+    use crate::{
+        diff_count::{sim_hash::SIM_BUCKETS, GeoDiffCount7},
+        test_rng::prng_test_harness,
+    };
+
+    #[test]
+    fn sim_hash_iter_min_matches() {
+        prng_test_harness(100, |rng| {
+            let i = rng.random_range(0..1000);
+            let filter = GeoDiffCount7::pseudorandom_filter(i);
+            let expected_diff = rng.random_range(0..i);
+            let (iter, min_matches) = filter.sim_hashes_search(expected_diff);
+            let actual_count = iter.count();
+            let expected_min_matches = actual_count
+                .saturating_sub(expected_diff)
+                .max(SIM_BUCKETS / 2);
+            assert_eq!(min_matches, expected_min_matches)
+        });
+    }
+}