refactor: move spec helpers to spec/lib (#37010)

Co-authored-by: Milan Burda <miburda@microsoft.com>

spec/lib/window-helpers.ts

@@ -0,0 +1,47 @@
+import { expect } from 'chai';
+import { BrowserWindow } from 'electron/main';
+import { emittedOnce } from './events-helpers';
+
+async function ensureWindowIsClosed (window: BrowserWindow | null) {
+  if (window && !window.isDestroyed()) {
+    if (window.webContents && !window.webContents.isDestroyed()) {
+      // If a window isn't destroyed already, and it has non-destroyed WebContents,
+      // then calling destroy() won't immediately destroy it, as it may have
+      // <webview> children which need to be destroyed first. In that case, we
+      // await the 'closed' event which signals the complete shutdown of the
+      // window.
+      const isClosed = emittedOnce(window, 'closed');
+      window.destroy();
+      await isClosed;
+    } else {
+      // If there's no WebContents or if the WebContents is already destroyed,
+      // then the 'closed' event has already been emitted so there's nothing to
+      // wait for.
+      window.destroy();
+    }
+  }
+}
+
+export const closeWindow = async (
+  window: BrowserWindow | null = null,
+  { assertNotWindows } = { assertNotWindows: true }
+) => {
+  await ensureWindowIsClosed(window);
+
+  if (assertNotWindows) {
+    const windows = BrowserWindow.getAllWindows();
+    try {
+      expect(windows).to.have.lengthOf(0);
+    } finally {
+      for (const win of windows) {
+        await ensureWindowIsClosed(win);
+      }
+    }
+  }
+};
+
+export async function closeAllWindows () {
+  for (const w of BrowserWindow.getAllWindows()) {
+    await closeWindow(w, { assertNotWindows: false });
+  }
+}