def sign_in(conn, %{"email" => email, "password" => password}) do
    case Whatever.Auth.authenticate_user(email, password) do
      {:ok, user} ->
        conn
        |> put_session(:current_user_id, user.id)
        |> put_status(:ok)
        |> render(WhateverWeb.UserView, "sign_in.json", user: user)

      {:error, message} ->
        conn
        |> delete_session(:current_user_id)
        |> put_status(:unauthorized)
        |> render(WhateverWeb.ErrorView, "401.json", message: message)
    end
end

curl -H "Content-Type: application/json" -X POST -d '{"email":"user@test.com","password":"pass"}' http://localhost:4000/api/users/sign_in -c cookies.txt -b cookies.txt -i
> {"data":{"user":{"id":2,"email":"user@test.com"}}}%

def sign_in(conn, user) do
  conn
  |> bypass_through(Whatever.Router, :api)
  |> post("/api/users/sign_in", %{email: user.email, password: user.password})
  |> put_session(:current_user_id, user.id)
  |> send_resp(:ok, "")
  |> recycle()
end

test "renders user when user credentials are good", %{conn: conn, user: user} do
  conn
  |> assign(:current_user_id, user.id) # or use sign_in(user.email, user.password)
  |> recycle()
  conn = delete conn, user_path(conn, :sign_out)
  assert json_response(conn, 200)["data"] == %{
    "message" => "Signed out"}
end

1) test sign_out user renders user when user credentials are good (WhateverWeb.UserControllerTest)
 test/whatever_web/controllers/user_controller_test.exs:107
 ** (RuntimeError) expected response with status 200, got: 401, with body:
 {"errors":{"detail":"Unauthorized"}}