Universal unit testing (#125)

* Separate window by environment
* Install Karma
* Rename Web Components build rules
* Separate test files by environment
* Add override modifier
* Gather risky functions that interact with HTML elements in one place

javascript/karma.conf.js

@@ -0,0 +1,31 @@
+/**
+ * @license
+ * Copyright 2023 Google LLC
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module.exports = function (config) {
+  config.set({
+    basePath: '',
+    frameworks: ['jasmine'],
+    files: ['bundle/tests/*.js'],
+    reporters: ['progress'],
+    port: 9876,
+    colors: true,
+    logLevel: config.LOG_INFO,
+    autoWatch: false,
+    browsers: ['ChromeHeadless'],
+    singleRun: true,
+    concurrency: Infinity,
+  });
+};