fix(tests): source maps for Karma

karma.conf.js

         preprocessors: {
             'node_modules/core-js/**': [ 'webpack' ],
             './index.js': [ 'webpack' ],
-            './**/*.spec.js': [ 'webpack' ]
+            './**/*.spec.js': [ 'webpack', 'sourcemap' ]
         },
 
         // test results reporter to use

package-lock.json

         "jasmine-core": "^3.5.0"
       }
     },
+    "karma-sourcemap-loader": {
+      "version": "0.3.7",
+      "resolved": "https://registry.npmjs.org/karma-sourcemap-loader/-/karma-sourcemap-loader-0.3.7.tgz",
+      "integrity": "sha1-kTIsd/jxPUb+0GKwQuEAnUxFBdg=",
+      "dev": true,
+      "requires": {
+        "graceful-fs": "^4.1.2"
+      }
+    },
     "karma-webpack": {
       "version": "4.0.2",
       "resolved": "https://registry.npmjs.org/karma-webpack/-/karma-webpack-4.0.2.tgz",

package.json

     "karma": "5.1.1",
     "karma-chrome-launcher": "3.1.0",
     "karma-jasmine": "3.1.1",
+    "karma-sourcemap-loader": "0.3.7",
     "karma-webpack": "4.0.2",
     "string-replace-loader": "2.1.1",
     "webpack": "4.43.0",

webpack.config.js

         || process.argv.indexOf('--optimize-minimize') !== -1;
 
 const config = {
-    devtool: 'source-map',
+    // The inline-source-map is used to allow debugging the unit tests with Karma
+    devtool: minimize ? 'source-map' : 'inline-source-map',
     mode: minimize ? 'production' : 'development',
     module: {
         rules: [ {