diff --git a/.gitignore b/.gitignore
index 107b5bb36..02c4fcd79 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,10 @@
 *.csv
 *.mmdb
 *.svg
+
+# Snapshots
+## ... large
+*.full.snap
+
+#  ... unreviewed
+*.snap.new
diff --git a/milli/src/documents/mod.rs b/milli/src/documents/mod.rs
index c1580309a..5c83991c2 100644
--- a/milli/src/documents/mod.rs
+++ b/milli/src/documents/mod.rs
@@ -190,6 +190,17 @@ pub fn documents_batch_reader_from_objects(
     DocumentsBatchReader::from_reader(std::io::Cursor::new(builder.into_inner().unwrap())).unwrap()
 }
 
+#[cfg(test)]
+pub fn batch_reader_from_documents(
+    documents: &[Object],
+) -> DocumentsBatchReader<std::io::Cursor<Vec<u8>>> {
+    let mut builder = DocumentsBatchBuilder::new(Vec::new());
+    for object in documents {
+        builder.append_json_object(&object).unwrap();
+    }
+    DocumentsBatchReader::from_reader(std::io::Cursor::new(builder.into_inner().unwrap())).unwrap()
+}
+
 #[cfg(test)]
 mod test {
     use std::io::Cursor;
diff --git a/milli/src/snapshot_tests.rs b/milli/src/snapshot_tests.rs
index 77eeeb159..a881a155e 100644
--- a/milli/src/snapshot_tests.rs
+++ b/milli/src/snapshot_tests.rs
@@ -30,7 +30,7 @@ pub fn default_db_snapshot_settings_for_test(name: Option<&str>) -> insta::Setti
 
 #[macro_export]
 macro_rules! db_snap {
-    ($index:ident, $db_name:ident, $name:literal) => {
+    ($index:ident, $db_name:ident, $name:expr) => {
         let settings = $crate::snapshot_tests::default_db_snapshot_settings_for_test(Some(
             &format!("{}", $name),
         ));
diff --git a/milli/src/update/facets.rs b/milli/src/update/facets.rs
index 5892123eb..981fa819c 100644
--- a/milli/src/update/facets.rs
+++ b/milli/src/update/facets.rs
@@ -342,3 +342,91 @@ fn write_string_entry(
     writer.insert(&key, &data)?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use std::num::NonZeroUsize;
+
+    use crate::{db_snap, documents::batch_reader_from_documents, index::tests::TempIndex};
+
+    #[test]
+    fn test_facets_number() {
+        let test =
+            |name: &str, group_size: Option<NonZeroUsize>, min_level_size: Option<NonZeroUsize>| {
+                let mut index = TempIndex::new_with_map_size(4096 * 1000 * 10); // 40MB
+                index.index_documents_config.autogenerate_docids = true;
+                index.index_documents_config.facet_level_group_size = group_size;
+                index.index_documents_config.facet_min_level_size = min_level_size;
+
+                index
+                    .update_settings(|settings| {
+                        settings.set_filterable_fields(
+                            IntoIterator::into_iter(["facet".to_owned(), "facet2".to_owned()])
+                                .collect(),
+                        );
+                    })
+                    .unwrap();
+
+                let mut documents = vec![];
+                for i in 0..1_000 {
+                    documents.push(serde_json::json!({ "facet": i }).as_object().unwrap().clone());
+                }
+                for i in 0..100 {
+                    documents.push(serde_json::json!({ "facet2": i }).as_object().unwrap().clone());
+                }
+                let documents = batch_reader_from_documents(&documents);
+
+                index.add_documents(documents).unwrap();
+
+                db_snap!(index, facet_id_f64_docids, name);
+            };
+
+        test("default", None, None);
+        test("tiny_groups_tiny_levels", NonZeroUsize::new(1), NonZeroUsize::new(1));
+        test("small_groups_small_levels", NonZeroUsize::new(2), NonZeroUsize::new(2));
+        test("small_groups_large_levels", NonZeroUsize::new(2), NonZeroUsize::new(128));
+        test("large_groups_small_levels", NonZeroUsize::new(16), NonZeroUsize::new(2));
+        test("large_groups_large_levels", NonZeroUsize::new(16), NonZeroUsize::new(256));
+    }
+
+    #[test]
+    fn test_facets_string() {
+        let test = |name: &str,
+                    group_size: Option<NonZeroUsize>,
+                    min_level_size: Option<NonZeroUsize>| {
+            let mut index = TempIndex::new_with_map_size(4096 * 1000 * 10); // 40MB
+            index.index_documents_config.autogenerate_docids = true;
+            index.index_documents_config.facet_level_group_size = group_size;
+            index.index_documents_config.facet_min_level_size = min_level_size;
+
+            index
+                .update_settings(|settings| {
+                    settings.set_filterable_fields(
+                        IntoIterator::into_iter(["facet".to_owned(), "facet2".to_owned()])
+                            .collect(),
+                    );
+                })
+                .unwrap();
+
+            let mut documents = vec![];
+            for i in 0..100 {
+                documents.push(
+                    serde_json::json!({ "facet": format!("s{i:X}") }).as_object().unwrap().clone(),
+                );
+            }
+            for i in 0..10 {
+                documents.push(
+                    serde_json::json!({ "facet2": format!("s{i:X}") }).as_object().unwrap().clone(),
+                );
+            }
+            let documents = batch_reader_from_documents(&documents);
+
+            index.add_documents(documents).unwrap();
+
+            db_snap!(index, facet_id_string_docids, name);
+        };
+
+        test("default", None, None);
+        test("tiny_groups_tiny_levels", NonZeroUsize::new(1), NonZeroUsize::new(1));
+    }
+}
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_number/default/facet_id_f64_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_number/default/facet_id_f64_docids.hash.snap
new file mode 100644
index 000000000..373455db6
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_number/default/facet_id_f64_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+587899707db2848da3f18399e14ed4d0
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_number/large_groups_large_levels/facet_id_f64_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_number/large_groups_large_levels/facet_id_f64_docids.hash.snap
new file mode 100644
index 000000000..c3415c320
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_number/large_groups_large_levels/facet_id_f64_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+02bbf2ca1663cccea0e4c06d5ad06a45
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_number/large_groups_small_levels/facet_id_f64_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_number/large_groups_small_levels/facet_id_f64_docids.hash.snap
new file mode 100644
index 000000000..78dad29f1
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_number/large_groups_small_levels/facet_id_f64_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+e68ea591e1af3e53e544dff9a1648e88
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_number/small_groups_large_levels/facet_id_f64_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_number/small_groups_large_levels/facet_id_f64_docids.hash.snap
new file mode 100644
index 000000000..61a5908f4
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_number/small_groups_large_levels/facet_id_f64_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+12a4bb0f5b95d7629c2b9a915150c0cf
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_number/small_groups_small_levels/facet_id_f64_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_number/small_groups_small_levels/facet_id_f64_docids.hash.snap
new file mode 100644
index 000000000..961346de5
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_number/small_groups_small_levels/facet_id_f64_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+6438e94bc7fada13022e0efccdf294e0
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_number/tiny_groups_tiny_levels/facet_id_f64_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_number/tiny_groups_tiny_levels/facet_id_f64_docids.hash.snap
new file mode 100644
index 000000000..2b7c1ef9c
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_number/tiny_groups_tiny_levels/facet_id_f64_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+5348bbc46b5384455b6a900666d2a502
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_string/default/facet_id_string_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_string/default/facet_id_string_docids.hash.snap
new file mode 100644
index 000000000..901b86255
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_string/default/facet_id_string_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+faddef9eae5f2efacfec51f20f2e8cd6
diff --git a/milli/src/update/snapshots/update/facets.rs/test_facets_string/tiny_groups_tiny_levels/facet_id_string_docids.hash.snap b/milli/src/update/snapshots/update/facets.rs/test_facets_string/tiny_groups_tiny_levels/facet_id_string_docids.hash.snap
new file mode 100644
index 000000000..aa6c85461
--- /dev/null
+++ b/milli/src/update/snapshots/update/facets.rs/test_facets_string/tiny_groups_tiny_levels/facet_id_string_docids.hash.snap
@@ -0,0 +1,4 @@
+---
+source: milli/src/update/facets.rs
+---
+ddb8fc987c5dc892337682595043858e