How to set session in phoenix controller tests

phoenix_session_test.md

If you are reading this, you probably tried to write code like this

test "testing session" do
  build_conn()
  |> put_session(:user_id, 234)
  |> get("/")
  ...
  end

And got this exception:

(ArgumentError) session not fetched, call fetch_session/2

The reason for this error is that Plug expects session to be initialized before allowing any access. One way to solve it is to add the following to support/conn_case.ex

  using do
    quote do
    
      ... #don't add this line :)
      
      def session_conn() do
        build_conn() |> Plug.Test.init_test_session(%{})
      end
    end
  end

Now your tests can use session_conn() to build a Plug.Conn with initialized session. For example:

test "testing session" do
  session_conn()
  |> put_session(:user_id, 234)
  |> get("/")
  ...
  end