25th May 2023 (UTC)
Some customers wanted to be able to match their synthetic tests to their server-side logs and monitoring applications, so to help them we've added the %TEST_ID% variable to synthetic scripting.
%TEST_ID% contains the id of the current test e.g. 230524_1F_1bff7967655cdf8ec75704406a3f2819, and can be added as query parameters, headers, cookies etc.
Adding the test id as a query parameter:
Adding the test id to a cookie
setCookie %ORIGIN% tag=%TEST_ID%
Variables can help make synthetic scripts re-usable and reliable and you can find out more about them in our scripting reference
The measurement of Cumulative Layout Shift (CLS) now uses the windowed measuring approach that RUM already uses Evolving the CLS metric
Some tests may see CLS values improve slightly as a result of this change, but most values won't change.
Chrome has a long-standing bug that incorrectly marks some layout shifts as having user input. If a layout shift is caused by user input, it should be ignored when calculating CLS. This often leads to a low CLS score even though the page has visible layout shifts.
Since synthetic testing has no actual users interacting with the page, we've ignored the has_user_input flag when calculating windowed CLS.
For a synthetic test, you should see greater consistency between the layout shifts and CLS. You might also see an increase in your overall CLS as layout shifts that were incorrectly ignored are now included.