specs: migrate from features to system specs

System specs have been available since Rails 5.1, and are better
integrated with the Rails framework.

- Rename `spec/features` to `spec/system`
- Rename `feature do` to `describe do`
- Configure Capybara for system specs

Steps mostly taken from https://medium.com/table-xi/a-quick-guide-to-rails-system-tests-in-rspec-b6e9e8a8b5f6

spec/system/france_connect/france_connect_particulier_spec.rb

@@ -0,0 +1,131 @@
+describe 'France Connect Particulier Connexion' do
+  let(:code) { 'plop' }
+  let(:given_name) { 'titi' }
+  let(:family_name) { 'toto' }
+  let(:birthdate) { '20150821' }
+  let(:gender) { 'M' }
+  let(:birthplace) { '1234' }
+  let(:email) { 'plop@plop.com' }
+  let(:france_connect_particulier_id) { 'blabla' }
+
+  let(:user_info) do
+    {
+      france_connect_particulier_id: france_connect_particulier_id,
+      given_name: given_name,
+      family_name: family_name,
+      birthdate: birthdate,
+      birthplace: birthplace,
+      gender: gender,
+      email_france_connect: email
+    }
+  end
+
+  context 'when user is on login page' do
+    before { visit new_user_session_path }
+
+    scenario 'link to France Connect is present' do
+      expect(page).to have_css('.france-connect-login-button')
+    end
+
+    context 'and click on france connect link' do
+      context 'when authentification is ok' do
+        before do
+          allow_any_instance_of(FranceConnectParticulierClient).to receive(:authorization_uri).and_return(france_connect_particulier_callback_path(code: code))
+          allow(FranceConnectService).to receive(:retrieve_user_informations_particulier).and_return(france_connect_information)
+        end
+
+        context 'when no user is linked' do
+          let(:france_connect_information) { build(:france_connect_information, user_info) }
+
+          context 'and no user has the same email' do
+            before { page.find('.france-connect-login-button').click }
+
+            scenario 'he is redirected to user dossiers page' do
+              expect(page).to have_content('Dossiers')
+              expect(User.find_by(email: email)).not_to be nil
+            end
+          end
+
+          context 'and an user exists with the same email' do
+            let!(:user) { create(:user, email: email, password: 'my-s3cure-p4ssword') }
+
+            before do
+              page.find('.france-connect-login-button').click
+            end
+
+            scenario 'he is redirected to the merge page' do
+              expect(page).to have_content('Fusion des comptes')
+            end
+
+            scenario 'it merges its account' do
+              page.find('#it-is-mine').click
+              fill_in 'password', with: 'my-s3cure-p4ssword'
+              click_on 'Fusionner les comptes'
+
+              expect(page).to have_content('Dossiers')
+            end
+
+            scenario 'it uses another email that belongs to nobody' do
+              page.find('#it-is-not-mine').click
+              fill_in 'email', with: 'new_email@a.com'
+              click_on 'Utiliser ce mail'
+
+              expect(page).to have_content('Dossiers')
+            end
+
+            context 'and the user wants an email that belongs to another account', js: true do
+              let!(:another_user) { create(:user, email: 'an_existing_email@a.com', password: 'my-s3cure-p4ssword') }
+
+              scenario 'it uses another email that belongs to another account' do
+                page.find('#it-is-not-mine').click
+                fill_in 'email', with: 'an_existing_email@a.com'
+                click_on 'Utiliser ce mail'
+
+                expect(page).to have_css('#password-for-another-account', visible: true)
+
+                within '.new-account-password-confirmation' do
+                  fill_in 'password', with: 'my-s3cure-p4ssword'
+                  click_on 'Fusionner les comptes'
+                end
+
+                expect(page).to have_content('Dossiers')
+              end
+            end
+          end
+        end
+
+        context 'when a user is linked' do
+          let!(:france_connect_information) do
+            create(:france_connect_information, :with_user, user_info.merge(created_at: Time.zone.parse('12/12/2012'), updated_at: Time.zone.parse('12/12/2012')))
+          end
+
+          before { page.find('.france-connect-login-button').click }
+
+          scenario 'he is redirected to user dossiers page' do
+            expect(page).to have_content('Dossiers')
+          end
+
+          scenario 'the updated_at date is well updated' do
+            expect(france_connect_information.reload.updated_at).not_to eq(france_connect_information.created_at)
+          end
+        end
+      end
+
+      context 'when authentification is not ok' do
+        before do
+          allow_any_instance_of(FranceConnectParticulierClient).to receive(:authorization_uri).and_return(france_connect_particulier_callback_path(code: code))
+          allow(FranceConnectService).to receive(:retrieve_user_informations_particulier) { raise Rack::OAuth2::Client::Error.new(500, error: 'Unknown') }
+          page.find('.france-connect-login-button').click
+        end
+
+        scenario 'he is redirected to login page' do
+          expect(page).to have_css('.france-connect-login-button')
+        end
+
+        scenario 'error message is displayed' do
+          expect(page).to have_content(I18n.t('errors.messages.france_connect.connexion'))
+        end
+      end
+    end
+  end
+end