Migrate to use System Tests

[seanpdoyle]

Migrate from the rspec-rails-provided Feature Tests, to the
Rails-provided System Tests.

The most beneficial outcome of this migration is the ability to rely on
use_transactional_fixtures = true in
browser-driven (JavaScript-enabled).

In order to be System Test compatible, this commit replaces test block
declarations made with feature with RSpec.describe, along with calls
to scenario with it.

In order to continue to support rails@4.2 and rails@5.0, the test
harness must elect to run type: :feature tests when
[ActionDispatch::SystemTestCase][system-test-care] is not declared.

In those cases, to preserve compatibility:

• pass type: :feature instead of type: :system to tests declared in
  spec/system
• require database_cleaner gem, along with Feature-test compatible
  configuration

To achieve this, this commit introduces the SYSTEM_TEST constant,
which refers to the correct type: option: :feature for older
versions of Rails, :system for newer versions.

Once support for rails@4.2 and rails@5.0 is dropped, these
declarations can be removed, and type: SYSTEM_TEST options can be
search-and-replaced with type: :system.

[nickcharlton]

@seanpdoyle, is this something you'd like to continue with? I realise it's been a while and there's a few conflicts but I'm not adverse to switching to use the new system tests.

[seanpdoyle]

@nickcharlton wow, I've forgotten about this. I don't have enough context on the codebase to estimate the effort involved in resolving these conflicts.

If you don't see a direct path toward resolution, we could close this.

That being said, I do think that adopting System Tests and Chromedriver would be valuable.

[nickcharlton]

Hah, no worries!

I'm going to close this for now, as I'm not really sure either how much more work there would be. Since, we have switched to Chromedriver, so that's been a big improvement anyway. Thanks for opening this way back when!