Adds Group SAML test button

Makes it easier to try out different configurations
while testing Group SAML settings.

ee/app/views/groups/saml_providers/_form.html.haml

@@ -26,3 +26,5 @@
 
     .form-actions
       = f.submit _("Save changes"), class: 'btn btn-success qa-save-changes-button'
+      .pull-right
+        = render 'test_button', saml_provider: @saml_provider

ee/app/views/groups/saml_providers/_test_button.html.haml

+- if saml_provider.persisted?
+  = saml_link_for_provider 'Test SAML SSO', saml_provider, redirect: request.url

ee/changelogs/unreleased/jej-group-saml-test-button.yml

+---
+title: Add test button to Group SAML settings
+merge_request: 5622
+author:
+type: changed

ee/lib/omni_auth/strategies/group_saml.rb

@@ -34,6 +34,18 @@ module OmniAuth
       def self.callback?(env)
         env['PATH_INFO'] =~ Gitlab::PathRegex.saml_callback_regex
       end
+
+      def mock_redirect_relay_state
+        setup_phase
+
+        redirect(request.params[relay_state_key])
+      end
+
+      private
+
+      def relay_state_key
+        options[:idp_sso_target_url_runtime_params].key(:RelayState) || 'RelayState'
+      end
     end
   end
 end

ee/spec/features/groups/saml_providers_spec.rb

@@ -17,6 +17,10 @@ describe 'SAML provider settings' do
     click_button('Save changes')
   end
 
+  def test_sso
+    click_link('Test SAML SSO')
+  end
+
   def stub_saml_config
     stub_licensed_features(group_saml: true)
     allow(Devise).to receive(:omniauth_providers).and_return(%i(group_saml))
@@ -72,6 +76,35 @@ describe 'SAML provider settings' do
         expect(login_url).to end_with "/groups/#{group.full_path}/-/saml/sso"
       end
     end
+
+    describe 'test button' do
+      let!(:saml_provider) { create(:saml_provider, group: group) }
+
+      before do
+        sign_in(user)
+        allow_any_instance_of(OmniAuth::Strategies::GroupSaml).to receive(:callback_url) { callback_path }
+      end
+
+      it 'POSTs to the SSO path for the group' do
+        visit group_saml_providers_path(group)
+
+        test_sso
+
+        expect(current_path).to eq callback_path
+      end
+
+      it 'sets RelayState to redirect back to settings page' do
+        visit group_saml_providers_path(group)
+
+        allow_any_instance_of(OmniAuth::Strategies::GroupSaml).to receive(:mock_request_call) do |group_saml_strategy|
+          group_saml_strategy.mock_redirect_relay_state
+        end
+
+        test_sso
+
+        expect(current_path).to eq group_saml_providers_path(group)
+      end
+    end
   end
 
   describe '#sso' do