chore: fixing coverage for karma using istanbul (open-telemetry#466)

api/karma.base.js

@@ -19,7 +19,12 @@ module.exports = {
   hostname: 'localhost',
   browsers: ['ChromeHeadless'],
   frameworks: ['mocha'],
-  reporters: ['spec'],
+  coverageIstanbulReporter: {
+    reports: ['json'],
+    dir: '.nyc_output',
+    fixWebpackSourcePaths: true
+  },
+  reporters: ['spec', 'coverage-istanbul'],
   files: ['test/index-webpack.ts'],
   preprocessors: { 'test/index-webpack.ts': ['webpack'] },
   webpackMiddleware: { noInfo: true }

api/karma.webpack.js

@@ -0,0 +1,43 @@
+/*!
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * 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
+ *
+ *      http://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.
+ */
+
+const webpackNodePolyfills = require('./webpack.node-polyfills.js');
+
+// This is the webpack configuration for browser Karma tests with coverage.
+module.exports = {
+  mode: 'development',
+  target: 'web',
+  output: { filename: 'bundle.js' },
+  resolve: { extensions: ['.ts', '.js'] },
+  devtool: 'inline-source-map',
+  module: {
+    rules: [
+      { test: /\.ts$/, use: 'ts-loader' },
+      {
+        enforce: 'post',
+        exclude: /(node_modules|\.test\.[tj]sx?$)/,
+        test: /\.ts$/,
+        use: {
+          loader: 'istanbul-instrumenter-loader',
+          options: { esModules: true }
+        }
+      },
+      // This setting configures Node polyfills for the browser that will be
+      // added to the webpack bundle for Karma tests.
+      { parser: { node: webpackNodePolyfills } }
+    ]
+  }
+};