Deal with non-existent managers group

We need to use `redirect_to` instead of `render` as otherwise, the
value of `action_name` is `create` instead of `new`. This
would bring a lot of issues in the rendering of the breadcrumbs.

Fixes #6313

src/api/app/controllers/webui/staging/workflows_controller.rb

@@ -22,12 +22,18 @@ def create
 
     staging_workflow.managers_group = Group.find_by(title: params[:managers_title])
 
+    unless staging_workflow.managers_group
+      flash[:error] = "Managers Group #{params[:managers_title]} couldn't be found"
+      redirect_to new_staging_workflow_path(project_name: @project)
+      return
+    end
+
     if staging_workflow.save
       flash[:success] = "Staging for #{@project} was successfully created"
       redirect_to staging_workflow_path(staging_workflow)
     else
       flash[:error] = "Staging for #{@project} couldn't be created"
-      render :new
+      redirect_to new_staging_workflow_path(project_name: @project)
     end
   end
 

src/api/spec/controllers/webui/staging/workflows_controller_spec.rb

@@ -65,15 +65,26 @@
       it { expect(flash[:success]).not_to be_nil }
     end
 
-    context 'when it fails to save' do
+    context 'when it cannot find the managers group' do
+      let(:params) { { project_name: project.name, managers_title: 'ItDoesNotExist' } }
+
+      before do
+        post :create, params: params
+      end
+
+      it { expect(response).to redirect_to(new_staging_workflow_path(project_name: project))  }
+      it { expect(flash[:error]).to eq("Managers Group #{params[:managers_title]} couldn't be found") }
+    end
+
+    context 'when it fails to save the staging workflow' do
       before do
         allow_any_instance_of(Staging::Workflow).to receive(:save).and_return(false)
-        post :create, params: { project: project.name }
+        post :create, params: { project: project.name, managers_title: managers_group.title }
       end
 
       it { expect(Staging::Workflow.count).to eq(0) }
-      it { expect(response).to render_template(:new) }
-      it { expect(flash[:error]).not_to be_nil }
+      it { expect(response).to redirect_to(new_staging_workflow_path(project_name: project)) }
+      it { expect(flash[:error]).to eq("Staging for #{project} couldn't be created") }
     end
   end