gecko-dev/browser/base/content/test/tabs/browser_preloadedBrowser_zoom.js

"use strict";

const ZOOM_CHANGE_TOPIC = "browser-fullZoom:location-change";

/**
 * Helper to check the zoom level of the preloaded browser
 */
async function checkPreloadedZoom(level, message) {
  // Clear up any previous preloaded to test a fresh version
  gBrowser.removePreloadedBrowser();
  gBrowser._createPreloadBrowser();

  // Wait for zoom handling of preloaded
  const browser = gBrowser._preloadedBrowser;
  await new Promise(resolve => Services.obs.addObserver(function obs(subject) {
    if (subject === browser) {
      Services.obs.removeObserver(obs, ZOOM_CHANGE_TOPIC);
      resolve();
    }
  }, ZOOM_CHANGE_TOPIC));

  is(browser.fullZoom, level, message);

  // Clean up for other tests
  gBrowser.removePreloadedBrowser();
}

add_task(async function test_default_zoom() {
  await checkPreloadedZoom(1, "default preloaded zoom is 1");
});

/**
 * Helper to open about:newtab and zoom then check matching preloaded zoom
 */
async function zoomNewTab(changeZoom, message) {
  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, "about:newtab");
  changeZoom();
  const level = tab.linkedBrowser.fullZoom;
  await BrowserTestUtils.removeTab(tab);

  await checkPreloadedZoom(level, `${message}: ${level}`);
}

add_task(async function test_preloaded_zoom_out() {
  await zoomNewTab(() => FullZoom.reduce(), "zoomed out applied to preloaded");
});

add_task(async function test_preloaded_zoom_in() {
  await zoomNewTab(() => {
    FullZoom.enlarge();
    FullZoom.enlarge();
  }, "zoomed in applied to preloaded");
});

add_task(async function test_preloaded_zoom_default() {
  await zoomNewTab(() => FullZoom.reduce(), "zoomed back to default applied to preloaded");
});