test that unknown zones don't store mapping keys

[#4942]
Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

activesupport/test/time_zone_test.rb

@@ -285,6 +285,11 @@ def test_unknown_zone_with_utc_offset
     assert_equal(-21_600, zone.utc_offset)
   end
 
+  def test_unknown_zones_dont_store_mapping_keys
+    ActiveSupport::TimeZone["bogus"]
+    assert !ActiveSupport::TimeZone.zones_map.key?("bogus")
+  end
+
   def test_new
     assert_equal ActiveSupport::TimeZone["Central Time (US & Canada)"], ActiveSupport::TimeZone.new("Central Time (US & Canada)")
   end