Solution_A.js

  $("ul#selected_lessons a").live("click", function(event) {
    event.preventDefault();
    $(this).closest("li").appendTo($("ul#available_lessons"));
    $("ul#available_lessons").sortable("refresh");
    $("ul#selected_lessons").sortable("refresh");
    $.post(
        $("ul#selected_lessons").data("update-url"),
        $("ul#selected_lessons").sortable("serialize"));
  });

Solution_A.rb

    it "should remove a lesson from a pathway" do
      pathway = create(:pathway)
      lesson  = create(:lesson, grade_level_id: pathway.grade_level_id)
      pathway.lessons << lesson

      pathway.lessons.reload.must_include lesson

      visit edit_pathway_path(pathway)
      page.click_on("remove")
      sleep 5

      pathway.lessons.reload.wont_include lesson
    end

Solution_B.js

  $("ul#selected_lessons a").live("click", function(event) {
    event.preventDefault();
    var li = $(this).closest("li").detach();
    $("ul#selected_lessons").sortable("refresh");
    $.post(
      $("ul#selected_lessons").data("update-url"),
      $("ul#selected_lessons").sortable("serialize"),
      function() {
        li.appendTo($("ul#available_lessons"));
        $("ul#available_lessons").sortable("refresh");
      }
    );
  });

Solution_B.rb

    it "should remove a lesson from a pathway" do
      pathway = create(:pathway)
      lesson  = create(:lesson, grade_level_id: pathway.grade_level_id)
      pathway.lessons << lesson

      pathway.lessons.reload.must_include lesson

      visit edit_pathway_path(pathway)
      page.click_on("remove")
      page.has_selector?("#available_lessons .handle").must_equal true

      pathway.lessons.reload.wont_include lesson
    end