diff --git a/haystack/testing/document_store.py b/haystack/testing/document_store.py
index 9cace29c798..17ec67d1817 100644
--- a/haystack/testing/document_store.py
+++ b/haystack/testing/document_store.py
@@ -1052,24 +1052,27 @@ def test_count_unique_metadata_by_filter_with_filter(document_store: DocumentSto
 
     @staticmethod
     def test_count_unique_metadata_by_filter_with_multiple_filters(document_store: DocumentStore):
-        """Test counting with multiple filters"""
+        """Test count_unique_metadata_by_filter() with multiple filters."""
         docs = [
-            Document(content="Doc 1", meta={"category": "A", "year": 2023}),
-            Document(content="Doc 2", meta={"category": "A", "year": 2024}),
-            Document(content="Doc 3", meta={"category": "B", "year": 2023}),
-            Document(content="Doc 4", meta={"category": "B", "year": 2024}),
+            Document(content="Doc 1", meta={"category": "B", "year": 2023, "status": "draft"}),
+            Document(content="Doc 2", meta={"category": "B", "year": 2023, "status": "draft"}),
+            Document(content="Doc 3", meta={"category": "B", "year": 2023, "status": "published"}),
+            Document(content="Doc 4", meta={"category": "B", "year": 2024, "status": "draft"}),
         ]
         document_store.write_documents(docs)
-        count = document_store.count_documents_by_filter(  # type:ignore[attr-defined]
+        # The compound filter matches three documents with duplicated values, so the counts only come
+        # out right when the store both applies the filter and properly counts the values.
+        counts = document_store.count_unique_metadata_by_filter(  # type:ignore[attr-defined]
             filters={
                 "operator": "AND",
                 "conditions": [
                     {"field": "meta.category", "operator": "==", "value": "B"},
                     {"field": "meta.year", "operator": "==", "value": 2023},
                 ],
-            }
+            },
+            metadata_fields=["status", "year"],
         )
-        assert count == 1
+        assert counts == {"status": 2, "year": 1}
 
 
 class GetMetadataFieldsInfoTest:
diff --git a/haystack/testing/document_store_async.py b/haystack/testing/document_store_async.py
index e8270381f34..fa469740a72 100644
--- a/haystack/testing/document_store_async.py
+++ b/haystack/testing/document_store_async.py
@@ -305,13 +305,15 @@ async def test_count_unique_metadata_by_filter_async_with_filter(document_store:
     async def test_count_unique_metadata_by_filter_async_with_multiple_filters(document_store: AsyncDocumentStore):
         """Test counting unique metadata asynchronously with multiple filters."""
         docs = [
-            Document(content="Doc 1", meta={"category": "A", "year": 2023}),
-            Document(content="Doc 2", meta={"category": "A", "year": 2024}),
-            Document(content="Doc 3", meta={"category": "B", "year": 2023}),
-            Document(content="Doc 4", meta={"category": "B", "year": 2024}),
+            Document(content="Doc 1", meta={"category": "B", "year": 2023, "status": "draft"}),
+            Document(content="Doc 2", meta={"category": "B", "year": 2023, "status": "draft"}),
+            Document(content="Doc 3", meta={"category": "B", "year": 2023, "status": "published"}),
+            Document(content="Doc 4", meta={"category": "B", "year": 2024, "status": "draft"}),
         ]
         await document_store.write_documents_async(docs)
 
+        # The compound filter matches three documents with duplicated values, so the counts only come
+        # out right when the store both applies the filter and properly counts the values.
         counts = await document_store.count_unique_metadata_by_filter_async(  # type:ignore[attr-defined]
             filters={
                 "operator": "AND",
@@ -320,9 +322,9 @@ async def test_count_unique_metadata_by_filter_async_with_multiple_filters(docum
                     {"field": "meta.year", "operator": "==", "value": 2023},
                 ],
             },
-            metadata_fields=["category", "year"],
+            metadata_fields=["status", "year"],
         )
-        assert counts == {"category": 1, "year": 1}
+        assert counts == {"status": 2, "year": 1}
 
 
 class DeleteByFilterAsyncTest:
diff --git a/releasenotes/notes/fix-count-unique-metadata-mixin-test-5415d442cdb70c15.yaml b/releasenotes/notes/fix-count-unique-metadata-mixin-test-5415d442cdb70c15.yaml
new file mode 100644
index 00000000000..8f36d5b4f36
--- /dev/null
+++ b/releasenotes/notes/fix-count-unique-metadata-mixin-test-5415d442cdb70c15.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed ``CountUniqueMetadataByFilterTest.test_count_unique_metadata_by_filter_with_multiple_filters``
+    in the document store testing mixins: it called ``count_documents_by_filter`` instead of
+    ``count_unique_metadata_by_filter``. The test now exercises the intended method with a compound
+    filter, matching its async counterpart.