stopServe() in testWithSpectron() throws setTimeout(...).unref is not a function

[thislooksfun]

Describe the bug
Calling stopServe() throws an exception setTimeout(...).unref is not a function.

To Reproduce
Minimal example:

import spectron from "spectron";
import testWithSpectron from "vue-cli-plugin-electron-builder/lib/testWithSpectron";
import chai from "chai";
import chaiAsPromised from "chai-as-promised";

chai.should();
chai.use(chaiAsPromised);

describe("Application launch", function() {
  let app;
  let stopServe;

  beforeEach(function() {
    return testWithSpectron(spectron).then(instance => {
      app = instance.app;
      stopServe = instance.stopServe;
    });
  }, 30000);

  beforeEach(function() {
    chaiAsPromised.transferPromiseness = app.transferPromiseness;
  });

  afterEach(function() {
    if (app && app.isRunning()) {
      return stopServe();
    }
  });

  it("opens a window", function() {
    return app.client
      .getWindowCount()
      .should.eventually.have.at.least(1)
      .browserWindow.isMinimized()
      .should.eventually.be.false.browserWindow.isVisible()
      .should.eventually.be.true.browserWindow.getBounds()
      .should.eventually.have.property("width")
      .and.be.above(0)
      .browserWindow.getBounds()
      .should.eventually.have.property("height")
      .and.be.above(0);
  });
});

Expected behavior
Calling stopServe() should not throw an error.

Screenshots
N/A

Environment (please complete the following information):

• OS and version: macOS 10.15.2 (19C57)
• node version: v12.14.1
• npm version: v6.13.4
• yarn version (if used): N/A
• vue-cli-plugin-electron-builder version: v2.0.0-beta.1
• electron version: v7.1.11
• other vue plugins used: See package.json
• custom config for vcp-electron-builder: N/A
• (if possible) link to your repo: https://github.com/thislooksfun/earthdawn

Additional context
This is due to a bug in execa that was fixed in v4.0.0.

[nklayman]

Unfortunately I cannot update to v4.0.0 as it requires node 10+. Since vue cli supports v8+, I don't want my plugin to be incompatible. Once vue cli requires v10+, I will upgrade execa.

[thislooksfun]

This renders testWithSpectron() useless as I can't close electron after the tests complete. Do you have any planned mitigation for this?

[nklayman]

I don't think there is anything I can really do, other than wait for vue cli to drop node 8 support. This shouldn't take too long as it is already officially deprecated. In the meantime, I will leave this as a beta release and mark this as a known issue. If you are okay with dropping node 8 support, you can use yarn resolutions to use execa v4.