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 initialize before allowing any access. One way to solve it is to add the following to support/conn_case.ex inside the (likely already existing) using quote blocks

  using do
    quote do
    
      ... #don't add this line :)
      
      def session_conn() do
        opts =
          Plug.Session.init(
            store: :cookie,
            key: "foobar",
            encryption_salt: "encrypted cookie salt",
            signing_salt: "signing salt",
            log: false,
            encrypt: false
          )
        build_conn()
        |> Plug.Session.call(opts)
        |> fetch_session()
      end
    end
  end

Now your tests can use session_conn() to build a Plug.Conn with initialized session. I like to put it in a function that setup can call

For example:

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

defp create_session_conn(_) do
  conn = session_conn()
  {:ok, conn: conn}
end