Update default puma server registration to try to ensure single mode

capybara.gemspec

@@ -37,6 +37,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency("cucumber", [">= 0.10.5"])
   s.add_development_dependency("minitest")
   s.add_development_dependency("rake")
+  s.add_development_dependency("puma")
   s.add_development_dependency("pry")
   s.add_development_dependency("erubi")  # dependency specification needed by rbx
 

lib/capybara.rb

@@ -448,7 +448,7 @@ end
 
 Capybara.register_server :puma do |app, port, host|
   require 'rack/handler/puma'
-  Rack::Handler::Puma.run(app, Host: host, Port: port, Threads: "0:4")
+  Rack::Handler::Puma.run(app, Host: host, Port: port, Threads: "0:4", workers: 0, daemon: false)
 end
 
 Capybara.configure do |config|

spec/capybara_spec.rb

@@ -79,6 +79,22 @@ RSpec.describe Capybara do
       Capybara.server(&server)
       expect(Capybara.server).to eq(server)
     end
+
+    it "should have :webrick registered" do
+      require 'rack/handler/webrick'
+      mock_app = double('app')
+      Capybara.server = :webrick
+      expect(Rack::Handler::WEBrick).to receive(:run)
+      Capybara.server.call(mock_app, 8000)
+    end
+
+    it "should have :puma registered" do
+      require 'rack/handler/puma'
+      mock_app = double('app')
+      Capybara.server = :puma
+      expect(Rack::Handler::Puma).to receive(:run)
+      Capybara.server.call(mock_app, 8000)
+    end
   end
 
   describe 'app_host' do