First a small "tale" about this addition proposal: 

I originally changed (replaced) this test to have a specification that would break when adding or removing `TRAVIS_` variables. It also had the advantage during "wip" phase to be intensively run as `bundle exec rspec spec/data/env_spec.rb`.

The full expectations about variable name and value are already well validated in https://github.com/travis-ci/travis-build/blob/master/spec/shared/script.rb#L4, that is used across all language specific scripts (see `spec/script/...`).

I'm thus not sure if it worth implement again the exhaustive matrix here. I also can revert it and stay with original 'includes travis env vars'.