This seems to be a "random" error introduced by the tests added @ MDL-68093.

Specially noticeable with Oracle, but any database can be affected potentially, we are getting these here and there:

Link:

1) core\grouplib_test::test_get_user_groups_with_visibility

Failed asserting that two arrays are equal.

--- Expected

+++ Actual

@@ @@

 Array (

-    0 => '1'

-    1 => '2'

-    2 => '3'

-    3 => '4'

+    0 => 3

+    1 => 4

+    2 => 1

+    3 => 2

 )

/var/www/html/lib/tests/grouplib_test.php:2124

/var/www/html/lib/phpunit/classes/advanced_testcase.php:94

It's clearly the typical problem of order not being guaranteed by groups_get_user_groups().

And there are two possible approaches to fix it:

1. If it's ok to force an ordering to happen, do it (ORDER by id or whatever) in the core function.
2. If really the order doesn't matter, then "relax" the test by using assertEqualsCanonicalizing, so only values are tested, irrespectively of the position.

Normally, 90% of times we just follow approach #1, guaranteeing the function returns ordered stuff.

But #2 is also ok if we aren't going to need any specific order ever.