UsersGroupsRightsManagementIT#editGroup is flickering

The functional test org.xwiki.administration.test.ui.AllIT$NestedUsersGroupsRightsManagementIT#editGroup fails intermittently.

Occurrence

• Seen locally on master (3fe0c7ae70d, plus test-only changes to other methods of the same class), HSQLDB, Tomcat, Firefox, while running AllIT$NestedUsersGroupsRightsManagementIT: 1 failure in the first run; the other 19 tests of the class passed.

Error

java.lang.AssertionError:
Expected: a collection containing "editGroup_backEndDevs"
     but: mismatches were: [... editGroup_Alice ..., ... editGroup_Bob ..., ... editGroup_frontEndDevs ...]
	at org.xwiki.livedata.test.po.TableLayoutElement.assertRow(TableLayoutElement.java:258)
	at org.xwiki.livedata.test.po.TableLayoutElement.assertRow(TableLayoutElement.java:243)
	at org.xwiki.administration.test.ui.UsersGroupsRightsManagementIT.editGroup(UsersGroupsRightsManagementIT.java:227)

Analysis

The failing step is in the "group edit modal from the administration" part: devsGroupModal.addUsers(alice).addGroups(backEndDevs), then assertRow("Member", backEndDevs). The members table already lists Alice (added just before) but not the backEndDevs sub-group, so either the second add was not applied or the table was not reloaded after it. Root cause not yet confirmed.