add tests, convert to using getters/setters

Author: rickeylev

api_notes.md

@@ -0,0 +1,11 @@
+:::{field} kwargs
+:type: dict[str, Any]
+
+Additional kwargs to use when building. This is to allow manipulations that
+aren't directly supported by the builder's API. The state of this dict
+may or may not reflect prior API calls, and subsequent API calls may
+modify this dict. The general contract is that modifications to this will
+be respected when `build()` is called, assuming there were no API calls
+in between.
+:::
+