test.js

setup(function(options) {
  options.phase = 'reboot';
});

afterEach(function(phase) {
  return new Promise(function(resolve, reject) {
    var marionette = phase.device.marionette;

    marionette
      .startSession()
      .then(function(client) {
        client.switchToFrame();

        client.executeAsyncScript(function() {
          var settings = window.wrappedJSObject.navigator.mozSettings;

          if (settings == null) {
            marionetteScriptFinished(new Error("Can't get settings after previous session"));
            return;
          }

          var lock = settings.createLock();
          var result = lock.set({
            'lockscreen.enabled': true
          });

          result.onsuccess = function() {
            marionetteScriptFinished(null, 'success!');
          };
          result.error = function(err) {
            marionetteScriptFinished(err, 'error!');
          };
        }, function(err, ret) {
          console.log(err);
          console.log(ret);
          client.deleteSession();
          resolve();
        });
      });
  });
});