Fix puma loading in Rails 5.1

[fables-tales]

No description provided.

[JonRowe]

This LGTM @samphippen, merge on green and get out a bugfix :)

[guilleiguaran]

If I understand this PR correctly it's disabling entirely system tests entirely if Puma is not present because it's a hard requirement for system tests in Rails 5.1, right?

IMO Puma should be the default for System tests but not a hard requirement and we must allow the use of alternatives. I'll try to improve this on Rails side to make this work even when puma gem isn't present (making Puma the default but allowing the use alternative servers as WebRick and Unicorn for SystemTestCase)

We aren't requiring to Puma gem directly in SystemTestCase anymore: rails/rails@50f6976

and Puma is set as default server through Capybara.server: https://github.com/rails/rails/blob/50f697664edf0d2deff22f3f1a1c8e01d54a74ca/actionpack/lib/action_dispatch/system_testing/server.rb#L23, in this way puma gem isn't required until it's used by Capybara.

I'll create a test app with rails master and rspec 3.7.0 to check if the error persists and hopefully, we can backport this to 5.1.x

[guilleiguaran]

I've created a test app with rails master, rspec 3.7.0, added a system spec and removed puma gem and after of setting in spec_helper.rb:

config.before(:suite)   { Capybara.server = :webrick }

The spec worked as expected.

[JonRowe]

@guilleiguaran any idea when that'll be released? And will it be a minor or patch level increment.

[ansonhoyt]

@guilleiguaran thanks for this. I was just trying out a system test with Capybara.server = :passenger, and noticed the hardcoded require "rack/handler/puma" in actionpack.

A 5.1 backport would be much appreciated, as it would let my tests more closely match production.