gecko-dev/browser/base/content/test/general/browser_backButtonFitts.js

/* Any copyright is dedicated to the Public Domain.
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

add_task(async function() {
  let firstLocation =
    "http://example.org/browser/browser/base/content/test/general/dummy_page.html";
  await BrowserTestUtils.openNewForegroundTab(gBrowser, firstLocation);

  await ContentTask.spawn(gBrowser.selectedBrowser, {}, async function() {
    // Push the state before maximizing the window and clicking below.
    content.history.pushState("page2", "page2", "page2");

    // While in the child process, add a listener for the popstate event here. This
    // event will fire when the mouse click happens.
    content.addEventListener(
      "popstate",
      function() {
        sendAsyncMessage("Test:PopStateOccurred", {
          location: content.document.location.href,
        });
      },
      { once: true }
    );
  });

  window.maximize();

  // Find where the nav-bar is vertically.
  var navBar = document.getElementById("nav-bar");
  var boundingRect = navBar.getBoundingClientRect();
  var yPixel = boundingRect.top + Math.floor(boundingRect.height / 2);
  var xPixel = 0; // Use the first pixel of the screen since it is maximized.

  let resultLocation = await new Promise(resolve => {
    window.messageManager.addMessageListener(
      "Test:PopStateOccurred",
      function statePopped(message) {
        window.messageManager.removeMessageListener(
          "Test:PopStateOccurred",
          statePopped
        );
        resolve(message.data.location);
      }
    );

    EventUtils.synthesizeMouseAtPoint(xPixel, yPixel, {}, window);
  });

  is(
    resultLocation,
    firstLocation,
    "Clicking the first pixel should have navigated back."
  );
  window.restore();

  gBrowser.removeCurrentTab();
});