Bug 1607984 - P11. Don't assume the page will be loaded synchronously. r=zombie

We must wait for the iframe created by extension1 to be fully loaded before we can attempt to send a message to it. So we send a message when it is ready, and suspend the execution until this message is received. Differential Revision: https://phabricator.services.mozilla.com/D70008
2020-04-15 15:37:11 +00:00 · 2020-04-15 15:37:11 +00:00 · 46e166596d
--- a/toolkit/components/extensions/test/xpcshell/test_ext_runtime_sendMessage_args.js
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_runtime_sendMessage_args.js
@ -22,6 +22,8 @@ add_task(async function() {
        browser.runtime.onMessage.addListener((msg, sender) => {
          browser.test.sendMessage("received-page", { msg, sender });
        });
+        // Let them know we're done loading the page.
+        browser.test.sendMessage("page-ready");
      },
      "page.html": `<!DOCTYPE html><meta charset="utf-8"><script src="page.js"></script>`,
    },
@ -37,6 +39,7 @@ add_task(async function() {
  });

  await Promise.all([extension1.startup(), extension2.startup()]);
+  await extension1.awaitMessage("page-ready");

  // Check that a message was sent within extension1.
  async function checkLocalMessage(msg) {