Updated the files.

my-app/node_modules/karma/context/main.js

@@ -0,0 +1,21 @@
+// Load in our dependencies
+var ContextKarma = require('./karma')
+
+// Resolve our parent window
+var parentWindow = window.opener || window.parent
+
+// Define a remote call method for Karma
+var callParentKarmaMethod = ContextKarma.getDirectCallParentKarmaMethod(parentWindow)
+
+// If we don't have access to the window, then use `postMessage`
+// DEV: In Electron, we don't have access to the parent window due to it being in a separate process
+// DEV: We avoid using this in Internet Explorer as they only support strings
+//   https://caniuse.com/?search=postmessage
+var haveParentAccess = false
+try { haveParentAccess = !!parentWindow.window } catch (err) { /* Ignore errors (likely permission errors) */ }
+if (!haveParentAccess) {
+  callParentKarmaMethod = ContextKarma.getPostMessageCallParentKarmaMethod(parentWindow)
+}
+
+// Define a window-scoped Karma
+window.__karma__ = new ContextKarma(callParentKarmaMethod)