Migrate from karma+mocha to jest

jest/__mocks__/intlMock.js

@@ -0,0 +1,22 @@
+/* eslint-env node */
+const path = require("path");
+const { transform } = require("../../webpack-utils/intl-loader");
+
+module.exports = {
+  /**
+   * @param {string} src - transformed module source code
+   * @param {string} filename - transformed module file path
+   * @param {{[key: string]: any}} config - jest config
+   * @param {{instrument: boolean}} options - additional options
+   *
+   * @return {string}
+   */
+  // eslint-disable-next-line no-unused-vars
+  process(src, filename, config, options) {
+    return transform(
+      src,
+      filename,
+      path.resolve(`${__dirname}/../../..`)
+    );
+  }
+};

jest/__mocks__/mockStrExport.js

@@ -0,0 +1 @@
+module.exports = 'test-file-stub';