Make organisation field searchable

This upgrades the organisations field in the page for inviting a new
user to use the accessible autocomplete module (with progressive
enhancement)

app/views/devise/invitations/new.html.erb

@@ -49,12 +49,23 @@
         autocomplete: "off",
       } %>
 
-      <%= render "govuk_publishing_components/components/select", {
-        id: "user_organisation_id",
-        name: "user[organisation_id]",
-        label: "Organisation",
-        options: options_for_organisation_select(selected: f.object.organisation_id)
-      } %>
+      <div data-module="accessible-autocomplete">
+        <%= render "govuk_publishing_components/components/select", {
+          id: "user_organisation_id",
+          name: "user[organisation_id]",
+          label: "Organisation",
+          options: options_for_organisation_select(selected: f.object.organisation_id)
+        } %>
+
+        <div class="govuk-button-group">
+          <%= render "govuk_publishing_components/components/button", {
+            text: "Clear selection",
+            type: "button",
+            classes: "js-autocomplete__clear-button",
+            secondary_solid: true
+          } %>
+        </div>
+      </div>
 
       <% if policy(User).assign_role? %>
         <%= render "govuk_publishing_components/components/select", {

test/integration/inviting_users_test.rb

@@ -384,4 +384,44 @@ class InvitingUsersTest < ActionDispatch::IntegrationTest
       end
     end
   end
+
+  context "with JavaScript enabled" do
+    setup do
+      use_javascript_driver
+
+      create(:organisation, name: "ABCDEF")
+      create(:organisation, name: "GHIJKL")
+      @organisation = create(:organisation, name: "MNOPQR")
+      create(:organisation, name: "STUVWX")
+      create(:organisation, name: "YZ1234")
+
+      superadmin = create(:superadmin_user)
+      visit root_path
+      signin_with(superadmin)
+    end
+
+    should "be able to invite a user" do
+      visit new_user_invitation_path
+      fill_in "Name", with: "H from Steps"
+      fill_in "Email", with: "h@from.steps"
+      select "Superadmin", from: "Role"
+
+      autocomplete_input_element = find(".autocomplete__input")
+      select_element = find("#user_organisation_id-select", visible: false)
+
+      assert_select_with_autocomplete(
+        autocomplete_input_element:,
+        select_element:,
+        option_text: @organisation.name,
+        option_value: @organisation.id.to_s,
+        unique_partial_string: "MNO",
+      )
+
+      click_button "Create user and send email"
+
+      new_user = User.find_by(email: "h@from.steps", role: Roles::Superadmin.name)
+      assert_not_nil new_user
+      assert_equal new_user.organisation, @organisation
+    end
+  end
 end