added a test case for the index

src/documents/tests/test_index.py

@@ -0,0 +1,14 @@
+from django.test import TestCase
+
+from documents.index import JsonFormatter
+
+
+class JsonFormatterTest(TestCase):
+
+    def setUp(self) -> None:
+        self.formatter = JsonFormatter()
+
+    def test_empty_fragments(self):
+        self.assertListEqual(self.formatter.format([]), [])
+
+