v4 improve coverage (#25945)

* Improve code coverage for our Button plugin

* improve coverage for our Alert plugin

* test tooltip update method

* test update and dispose for dropdown

* increase code coverage requirements

js/tests/unit/.eslintrc.json

@@ -7,7 +7,9 @@
   "globals": {
     "bootstrap": false,
     "sinon": false,
-    "Util": false
+    "Util": false,
+    "Alert": false,
+    "Button": false
   },
   "parserOptions": {
     "ecmaVersion": 5,