Return all mappings for a timezone id in `country_zones`

Some timezones like `Europe/London` have multiple mappings in
`ActiveSupport::TimeZone::MAPPING` so return all of them instead
of the first one found by using `Hash#value`. e.g:

  # Before
  ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh"]

  # After
  ActiveSupport::TimeZone.country_zones("GB") # => ["Edinburgh", "London"]

Fixes #31668.

1 files changed, 10 insertions, 0 deletions

diff --git a/activesupport/test/time_zone_test.rb b/activesupport/test/time_zone_test.rb
index 405c8f315b..63ca22efb5 100644
--- a/activesupport/test/time_zone_test.rb
+++ b/activesupport/test/time_zone_test.rb
@@ -756,6 +756,16 @@ class TimeZoneTest < ActiveSupport::TestCase
     assert_not_includes ActiveSupport::TimeZone.country_zones(:ru), ActiveSupport::TimeZone["Kuala Lumpur"]
   end
 
+  def test_country_zones_with_and_without_mappings
+    assert_includes ActiveSupport::TimeZone.country_zones("au"), ActiveSupport::TimeZone["Adelaide"]
+    assert_includes ActiveSupport::TimeZone.country_zones("au"), ActiveSupport::TimeZone["Australia/Lord_Howe"]
+  end
+
+  def test_country_zones_with_multiple_mappings
+    assert_includes ActiveSupport::TimeZone.country_zones("gb"), ActiveSupport::TimeZone["Edinburgh"]
+    assert_includes ActiveSupport::TimeZone.country_zones("gb"), ActiveSupport::TimeZone["London"]
+  end
+
   def test_country_zones_without_mappings
     assert_includes ActiveSupport::TimeZone.country_zones(:sv), ActiveSupport::TimeZone["America/El_Salvador"]
   end