Using @current_user in tests

I am still trying to run this test
setup do

    @comment = comments(:hello)
    @comment.commenter = "cleb"
    @comment.body = "hello"
    @comment.user_id = 1
    @cuser = User.find_by_id(session[:user_id])
test "should create comment" do

    assert_difference('Comment.count') do
      post :create, :comment => @comment.attributes, :user_id => 2

    assert_redirected_to comment_path(assigns(:comment))

I get this error

NoMethodError: undefined method `login' for nil:NilClass

This is from comments.controller

  def create
    @cuser = @current_user
    @user = User.find(params[:user_id])
    @user.comments.create(:user_id =>, :commenter =>
@cuser.login, :body => params[:comment][:body])
    respond_to do |format|
     format.html {redirect_to user_path}

How do I give the controller the required @current_user ?

(Derived from @current_user = User.find_by_id(session[:user_id])

What am I doing wrong?

The first thing is that you have not noticed that the error is
pointing out a bug in your code (as tests should do). You should be
checking in create that there is a user logged in (or not allowing
access to the action if no-one is logged in). So first you need to
add a test to check that the action cannot be accessed if no-one is
logged in. In order to get the test you have shown to pass you need
to effectively login a user by setting up the session. I have to go
so have not time to describe it but if you google for setting session
in rails tests then you should easily find it.