Adds a serializer test suite - project cereal (#5034)

* Setup basic architecture for tests

* Attribute tests

* Easy field tests added

* Work on tests

* Work on tests

* Work on tests

* Add mutation tests

* Fixup ID tests

* Add more mutator tests

* Fixup lint and typos

* Uncomment tests

* Use test helpers

* Small PR comments

* Use test helpers for setup and teardown

* Add TODOs and fixup types

* Fix types

* Actually fix types

tests/mocha/index.html

@@ -25,6 +25,8 @@
     <script src="../../blocks/math.js"></script>
     <script src="../../blocks/procedures.js"></script>
     <script src="../../blocks/text.js"></script>
+    <script src="../../blocks/variables.js"></script>
+    <script src="../../blocks/variables_dynamic.js"></script>
   </head>
   <style>
     #blocklyDiv {
@@ -90,6 +92,7 @@
     <script src="procedures_test_helpers.js"></script>
     <script src="procedures_test.js"></script>
     <script src="registry_test.js"></script>
+    <script src="serializer_test.js"></script>
     <script src="theme_test.js"></script>
     <script src="toolbox_test.js"></script>
     <script src="tooltip_test.js"></script>