Bug 1682035 - Fix test, ensure the event for waitForAttribute won't be missed. r=mkmelin

Differential Revision: https://phabricator.services.mozilla.com/D99561

--HG--
extra : rebase_source : d220cfe690043dd04dd8657528fe05eb2e39c34f

mail/test/browser/openpgp/browser_viewMessage.js

@@ -305,20 +305,30 @@ add_task(async function testUpdateMessageSignature() {
     return true;
   });
 
-  mc.click(mc.eid("viewSignatureKey"));
-  await dialogPromise;
-
-  // Wait for the icon to reload.
-  await BrowserTestUtils.waitForAttribute(
+  // To ensure we won't miss the attribute change event, set up a
+  // promise to wait for it, before running the actions that trigger it.
+  // Wait for any new attribute value, because a future bug might
+  // set an unexpected attribute.
+  let attributePromise = BrowserTestUtils.waitForAttribute(
     "signed",
     mc.window.document.getElementById("signedHdrIcon"),
-    "unverified"
+    null
   );
 
+  // This will open the key details, the domWindowOpened handler
+  // will catch it and execute the changes.
+  mc.click(mc.eid("viewSignatureKey"));
+
+  // Wait until we are done with keyDetailsDlg.
+  await dialogPromise;
+
+  // Wait for the signedHdrIcon state to change.
+  await attributePromise;
+
   // Verify the new acceptance level is correct.
   Assert.ok(
     OpenPGPTestUtils.hasSignedIconState(mc.window.document, "unverified"),
-    "signed unverified icon is displayed"
+    "signed unverified icon should be displayed"
   );
   close_window(mc);
 });