Regression testing is covered by the enrol_manual behat tests Setup This test requires that we have requests that take a much longer time to complete that later requests would, to simulate that we will modify the core_enrol_get_potential_users external function to take a minimum of 10 seconds. We will do that by adding the following lines of code to the get_potential_users method in /enrol/externallib.php: if ( strlen ( $search ) === 1) { sleep(10); } You can use one of the attached patch files to do this: For master: MDL-62194-master-simulate-long-request.diff For Moodle 3.4 and 3.5: MDL-62194-MOODLE_35_STABLE-and-MOODLE_£$_STABLE-simulate-long-request.diff Prerequisites A course ( Course 1 ) An Teacher enrolled on Course 1 Three users that have a matching start character in their name but then differentiate: Jane Eyre John Smith James Peach Testing that the autocomplete works Navigate to the Course 1 as Teacher In the hamburger menu select Participants Press Enrol users In the Select users search box start typing J Wait a second or two Then type ane so that the text in the box is Jane Stop typing Around 10 seconds after you completed step 4 you should see a list of users containing Jane Eyre , John Smith and James Peach (It may only show for half a second) Shortly after this the list of users should change to display Jane Eyre , verify that it no longer displays John Smith nor James Peach