Random PHP 7.1 test failures

[SergeyBiryukov]

Every few commits, there's now a random PHP 7.1 test failure on Travis, mostly off-by-one errors unrelated to the preceding commit. Started about 1 month ago, after August 20th.

Seems like either PHP 7.1 tests are for some reason more prone to random errors than other versions, or it's just more prominent now that random date/time failures from #45821 are fixed.

Creating a ticket just for reference, any ideas as to why this happens appreciated.

Some examples:

1) WP_Test_REST_Posts_Controller::test_get_items_search_query
Failed asserting that 6 matches expected 7.
/var/www/tests/phpunit/tests/rest-api/rest-posts-controller.php:459

1) WP_Test_REST_Posts_Controller::test_get_items_pagination_headers
Failed asserting that 49 matches expected 50.
/var/www/tests/phpunit/tests/rest-api/rest-posts-controller.php:1157

1) Tests_Canonical_PageOnFront::test with data set #3 ('/?page=1', '/')
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'/'
+'/?page=1'
/var/www/tests/phpunit/includes/testcase-canonical.php:268
/var/www/tests/phpunit/tests/canonical/pageOnFront.php:39
2) Tests_Query_MetaQuery::test_meta_query_single_query_compare_arithmetic_comparisons
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
-    0 => 2319
 )
/var/www/tests/phpunit/includes/abstract-testcase.php:658
/var/www/tests/phpunit/tests/query/metaQuery.php:162

1) Tests_Query::test_tag_querystring_single_term
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
     0 => 2022
-    1 => 2023
 )
/var/www/tests/phpunit/includes/abstract-testcase.php:658
/var/www/tests/phpunit/tests/query.php:321

1) Tests_Term_getTerms::test_wp_delete_term_should_invalidate_cache
Failed asserting that 1 matches expected 2.
/var/www/tests/phpunit/tests/term/getTerms.php:181

1) Tests_Query_VerbosePageRules::test_page_page_2
is_404 is true but is expected to be false. 
is_page is false but is expected to be true. 
is_paged is false but is expected to be true. 
is_singular is false but is expected to be true.
/var/www/tests/phpunit/includes/abstract-testcase.php:971
/var/www/tests/phpunit/tests/query/conditionals.php:327

1) Tests_Query_MetaQuery::test_meta_query_decimal_results
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
-    0 => 2414
 )
/var/www/tests/phpunit/includes/abstract-testcase.php:658
/var/www/tests/phpunit/tests/query/metaQuery.php:1170

1) Tests_Term_getTerms::test_hierarchical_true_with_parent
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
-    0 => 1277
-    1 => 1280
+    0 => 1280
 )
/var/www/tests/phpunit/includes/abstract-testcase.php:658
/var/www/tests/phpunit/tests/term/getTerms.php:2257

1) Tests_Query_SetupPostdata::test_secondary_query_nextpage
Failed asserting that two arrays are identical.
--- Expected
+++ Actual
@@ @@
 Array &0 (
-    0 => 'Post 1 Page 1'
-    1 => 'Post 1 Page 2'
+    0 => 'Post 2 Page 1'
+    1 => 'Post 2 Page 2'
 )
/var/www/tests/phpunit/tests/query/setupPostdata.php:249

1) Tests_Query_MetaQuery::test_meta_between_not_between
Failed asserting that 1 matches expected 2.
/var/www/tests/phpunit/tests/query/metaQuery.php:1537

1) Tests_Post_getPages::test_get_pages_non_hierarchical_non_empty_child_of
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
     0 => 1677
     1 => 1678
-    2 => 1679
 )
/var/www/tests/phpunit/includes/abstract-testcase.php:649
/var/www/tests/phpunit/tests/post/getPages.php:617

1) Tests_Post_Query::test_orderby_post__in_array
Failed asserting that two arrays are identical.
--- Expected
+++ Actual
@@ @@
 Array &0 (
-    0 => 428
-    1 => 426
-    2 => 429
+    0 => 426
+    1 => 429
 )
/var/www/tests/phpunit/tests/post/query.php:192