How do I intercept or mock ipcMain calls in an Electron + Mocha + WDIO e2e test for a Vue component?

Below is an explanation and some recommendations based on my understanding of Electron, WebdriverIO, and how your application initializes.

---

Why Your Mocks Aren’t Taking Effect

When your tests start running, your Electron app—including its main process—is already initialized. This means that by the time your test code calls something like

JAVASCRIPTCopied
await browser.electron.mock("ipcMain", "handle", "mocked");

your Vue component has already executed its checkIsAvailable() function. That function calls

JAVASCRIPTCopied
electronAPI.sendMessage("plugin:PathChecker:availability")

which in turn relies on the original IPC handler attached in the main process. In other words, you’re trying to override or intercept the main process behavior after it has been set up. So yes, you don’t have synchronous access to the main process objects once the app is running.

---

Options for Achieving Your Goals

Here are a few approaches to consider:

1. Mock on Startup:
   In order to mock IPC interactions you must do so before the Electron app (and your Vue component) initializes. One strategy is to add a condition in your main process code that checks for a test flag (for example, an environment variable) and then installs test-specific IPC mocks. This way, by the time your Vue code runs, the mocked handlers are already in place.

   JAVASCRIPTCopied
   // In your main process entry file (e.g., main.js)
   if (process.env.NODE_ENV === "test") {
       ipcMain.removeHandler("plugin:PathChecker:availability");
       ipcMain.handle("plugin:PathChecker:availability", async () => "mocked");
   }

2. Expose a Preload API for Test Control:
   Modify your preload script to export additional functionality so that test code (running in the renderer process) can trigger changes in the main process behavior early on. For example, you can expose a function that resets or installs new handlers. However, note that this still requires that your Vue component hasn’t made its IPC call or that you have some way to delay it until after the test’s setup code executes.

3. Mock the Renderer API:
   Since your Vue component depends on the globally declared electronAPI, you could mock that object in the renderer process rather than trying to change ipcMain in the main process. For instance, you might override electronAPI.sendMessage in your test setup before the Vue component mounts. This is generally easier because your test runner controls the renderer process.

   JAVASCRIPTCopied
   // In your test setup (executed before component rendering)
   await browser.execute(() => {
       window.electronAPI = {
           sendMessage: async (msg) => { return "mocked"; }
       };
   });

   This approach fits if your goal is simply to control what the Vue component receives.

4. Test the Main Process Separately:
   If you need to test IPC interactions in isolation, you might consider unit testing your main process logic with tools like Mocha and using dependency injection frameworks or modules like proxyquire to stub functions. Then you wouldn’t need to combine that with WDIO e2e tests.

---

Summary of Answers to Your Questions

• When using wdio + electron, is there a way to access variables on the main process?
  Not directly after startup. With WDIO you mainly interact with the renderer process. For the main process, you need to expose specific APIs via the preload script or in your Electron configuration.

• Is there a way to mock/fake ipc calls between the main process and the render process?
  Yes, but you must do it at app startup in the main process (or via a preload script) so that your mocks take effect before the renderer’s code runs. WDIO’s browser.electron.mock won’t change already set-up handlers.

• Is there a way to mock out functions on my Vue component before rendering it?
  Absolutely—if your goal is to change what data your component receives, you can override or stub the electronAPI (or whatever dependency injection you have) in the renderer process before the component mounts.

---

Recommendation

For your particular case—if controlling the Vue output is the main goal—it might be easiest to mock electronAPI.sendMessage in the renderer context rather than trying to override ipcMain in the main process. This lets you control the responses your component gets without having to rely on test hooks into the Electron main process.

Good luck, and feel free to ask for further clarification on any of these options!