Comment 29 for bug 1834072

The timezone test is expecting these to be equal:
 ["1911-12-31 23:59:59 -0036", -2192, "-0036", "-00:36", "-00:36:32"],
 ["1912-01-01 00:36:31 +0000", 0, "+0000", "+00:00", "+00:00:00"],

If I downgrade tzdata to the version that was released with xenial, then this test passes.

$ sudo apt install tzdata=2016d-0ubuntu0.16.04
sudo: unable to resolve host xenial-ruby23
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be DOWNGRADED:
  tzdata
(...)

$ ruby2.3 test/runner.rb test/ruby/test_time_tz.rb
Run options:

# Running tests:

Finished tests in 0.056691s, 1940.3463 tests/s, 18186.3371 assertions/s.
110 tests, 1031 assertions, 0 failures, 0 errors, 0 skips

ruby -v: ruby 2.3.1p112 (2016-04-26) [s390x-linux-gnu]

So I would say that a timezone rule changed since the xenial release, and the test wasn't updated.