Add tests for _flatten_dict.

tests/push/test_push_rule_evaluator.py

@@ -37,6 +37,29 @@
 from tests.test_utils.event_injection import create_event, inject_member_event
 
 
+class FlattenDictTestCase(unittest.TestCase):
+    def test_simple(self) -> None:
+        """Test a dictionary that isn't modified."""
+        input = {"foo": "abc"}
+        self.assertEqual(input, _flatten_dict(input))
+
+    def test_nested(self) -> None:
+        """Nested dictionaries become dotted paths."""
+        input = {"foo": {"bar": "abc"}}
+        self.assertEqual({"foo.bar": "abc"}, _flatten_dict(input))
+
+    def test_non_string(self) -> None:
+        """Booleans, ints, and nulls should be kept while other items are dropped."""
+        input: Dict[str, Any] = {
+            "foo": True,
+            "bar": 1,
+            "baz": None,
+            "fuzz": [],
+            "boo": {},
+        }
+        self.assertEqual({"foo": True, "bar": 1, "baz": None}, _flatten_dict(input))
+
+
 class PushRuleEvaluatorTestCase(unittest.TestCase):
     def _get_evaluator(
         self,