PYTHON-3028 $regex as a field name does not allow for non-string values (mongodb#807)

Author: juliusgeo

test/test_json_util.py

@@ -297,6 +297,15 @@ def test_regex_validation(self):
         doc = {"$regex": ""}
         self.assertIsInstance(json_util.loads(json.dumps(doc)), Regex)
 
+    def test_regex_validation(self):
+        non_str_types = [10, {}, []]
+        docs = [{"$regex": i} for i in non_str_types]
+        for doc in docs:
+            self.assertEqual(doc, json_util.loads(json.dumps(doc)))
+
+        doc = {"$regex": ""}
+        self.assertIsInstance(json_util.loads(json.dumps(doc)), Regex)
+
     def test_minkey(self):
         self.round_trip({"m": MinKey()})