Fix tests

I found some issues when trying to run the tests:

- Changes default timezone to the same as expected on tests. The date formatting as text is based on current timezone. The test failed on every timezone but Bangalore's.
- The exception message changes on different Ruby (and JRuby) versions. The exception message change depending on ruby version
- The serialization can be different depending (depending on active_suport version) but the content should always be the same.