Unified Runner overview

The Unified Runner is the next generation of the mabl testing service, built for more reliable and faster test execution. Reliability is achieved by unifying testing logic across the cloud, command-line interface, and mabl Desktop App.

The Unified Runner replaces the legacy implementation for executing browser tests in the cloud. At this time, running tests both locally and in the cloud with the Unified Runner is available for Chrome, Edge, Firefox, and Safari (WebKit).

You can also trigger local test runs using the Unified Runner via the mabl CLI or the mabl Desktop App.


In addition to the speed and reliability improvements, the following enhancements are available in the Unified Runner:

Testing setup

By default, plan runs and ad-hoc test runs are configured to run on the Unified Runner for Chrome. You can change settings for the Unified Runner in the browser settings.

Plan runs

Modify settings for plan runs in the Device settings section of the Edit Plan page.


Unified Runner for plans

Ad-hoc runs

Modify settings for ad-hoc runs in the Browsers section of the Ad-hoc run panel.

Unified Runner for ad-hoc cloud runs

Unified Runner for ad-hoc cloud runs


Legacy Runner sunset

The Unified Runner replaces the legacy implementation for executing browser tests in the cloud, which is known as the Legacy Runner.

You can learn more about the plan to sunset the Legacy Runner here.

Behavior changes

The following are known behavior changes in the Unified Runner.

Test creation:

  • Invalid CSS selectors that do not have a closing square bracket are no longer accepted. Existing tests need to be updated to properly format the CSS selector. For example, the Legacy Runner still allowed a CSS expression [aria-label="settings-portal-access". This is no longer accepted in the Unified Runner, and the expression must be updated to [aria-label="settings-portal-access"].
  • JavaScript syntax is enforced more strictly than the Legacy Runner. For example, variables must be explicitly defined.

Test execution:

  • When using XPath or CSS Selectors in a find elements step to enter text, the selector needs to find the input element in which you want to enter the text. In the Legacy Runner, if the element was not focused, it would go and try to type the text either way.
  • If the width and height are not specified, the Unified Runner defaults to a width of 1400 and a height of 1000 in the cloud. We recommend using a width and height that reflects the viewport size used when the test was created.

Identifying Unified test runs

To identify Unified test runs, hover your mouse over the browser icon anywhere test results are shown, including the Results page, the Test Output page, and the Plan Details page.


Identifying a Unified run on the Results page

When you hover your mouse over the browser icon, a tooltip appears with the following information:

  • Browser
  • Browser version: this version number corresponds to the version of the test at runtime.
  • Runner: Unified or Legacy

At the top of the Test Output page, check the Runner column to determine whether a browser test run used Unified or Legacy.


Identifying a Unified run on the Test Output page


The following limitations are present in the current version of the Unified Runner:

  • Link crawler tests are unsupported and use the Legacy Runner.
  • Internet Explorer is not supported.

Learn more about identifying Unified test runs, intelligent wait, and migrating to the Unified Runner.