Bug 1609906 - add test for about:downloads so we can't completely break it without noticing, r=mak

Differential Revision: https://phabricator.services.mozilla.com/D63106

--HG--
extra : moz-landing-system : lando

browser/components/downloads/test/browser/browser.ini

@@ -1,6 +1,7 @@
 [DEFAULT]
 support-files = head.js
 
+[browser_about_downloads.js]
 [browser_basic_functionality.js]
 [browser_first_download_panel.js]
 skip-if = os == "linux" # Bug 949434

browser/components/downloads/test/browser/browser_about_downloads.js

@@ -0,0 +1,38 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Ensure about:downloads actually works.
+ */
+add_task(async function test_about_downloads() {
+  await task_resetState();
+  registerCleanupFunction(task_resetState);
+
+  await setDownloadDir();
+
+  await task_addDownloads([
+    { state: DownloadsCommon.DOWNLOAD_FINISHED },
+    { state: DownloadsCommon.DOWNLOAD_PAUSED },
+  ]);
+  await BrowserTestUtils.withNewTab("about:downloads", async function(browser) {
+    await SpecialPowers.spawn(browser, [], async function() {
+      let box = content.document.getElementById("downloadsRichListBox");
+      ok(box, "Should have list of downloads");
+      is(box.children.length, 2, "Should have 2 downloads.");
+      for (let kid of box.children) {
+        let desc = kid.querySelector(".downloadTarget");
+        is(
+          desc.value,
+          "dm-ui-test.file",
+          "Should have listed the file name for this download."
+        );
+      }
+      info("Wait for the first item to be selected.");
+      await ContentTaskUtils.waitForCondition(() => {
+        return box.firstChild.selected;
+      }, "Timed out waiting for the first item to be selected.");
+    });
+  });
+});