Improve JSONEncoder test coverage (#47935)

tests/helpers/test_json.py

@@ -11,11 +11,17 @@ def test_json_encoder(hass):
     ha_json_enc = JSONEncoder()
     state = core.State("test.test", "hello")
 
+    # Test serializing a datetime
+    now = dt_util.utcnow()
+    assert ha_json_enc.default(now) == now.isoformat()
+
+    # Test serializing a set()
+    data = {"milk", "beer"}
+    assert sorted(ha_json_enc.default(data)) == sorted(list(data))
+
+    # Test serializing an object which implements as_dict
     assert ha_json_enc.default(state) == state.as_dict()
 
     # Default method raises TypeError if non HA object
     with pytest.raises(TypeError):
         ha_json_enc.default(1)
-
-    now = dt_util.utcnow()
-    assert ha_json_enc.default(now) == now.isoformat()