Implement tests to disable homepage settings

They were marked as pending.

Note Capybara doesn't support finding a button by its `aria-labelledby`
attribute, so we're using the ugly `click_button "Yes"`, like we did in
commit fabe97e50.

spec/system/admin/homepage/homepage_spec.rb

@@ -119,7 +119,56 @@ describe "Homepage", :admin do
       expect(page).to have_css(".legislation-process", count: 3)
     end
 
-    xscenario "Deactivate"
+    scenario "Deactivate proposals" do
+      Setting["homepage.widgets.feeds.proposals"] = true
+      create(:proposal)
+
+      visit admin_homepage_path
+
+      within("#widget_feed_#{proposals_feed.id}") do
+        click_button "Yes"
+
+        expect(page).to have_button "No"
+      end
+
+      visit root_path
+
+      expect(page).not_to have_content "Most active proposals"
+    end
+
+    scenario "Deactivate debates" do
+      Setting["homepage.widgets.feeds.debates"] = true
+      create(:debate)
+
+      visit admin_homepage_path
+
+      within("#widget_feed_#{debates_feed.id}") do
+        click_button "Yes"
+
+        expect(page).to have_button "No"
+      end
+
+      visit root_path
+
+      expect(page).not_to have_content "Most active debates"
+    end
+
+    scenario "Deactivate processes" do
+      Setting["homepage.widgets.feeds.processes"] = true
+      create(:legislation_process)
+
+      visit admin_homepage_path
+
+      within("#widget_feed_#{processes_feed.id}") do
+        click_button "Yes"
+
+        expect(page).to have_button "No"
+      end
+
+      visit root_path
+
+      expect(page).not_to have_content "Open processes"
+    end
   end
 
   scenario "Cards" do