Testing with Smokestack and AshAuthentication

There is ash_authentication but also ash_authentication_phoenix.
Got me confused recently.
Anyway, definitely check the latter. In ash authentication phoenix there is a test:

  test "sign_in routes allow a user to sign in", %{conn: conn} do
    Example.Accounts.User
    |> Ash.Changeset.for_create(:register_with_password, %{
      email: "zach@example.com",
      password: "so-secure!",
      password_confirmation: "so-secure!"
    })
    |> Ash.create!()

    conn = get(conn, "/sign-in")
    assert {:ok, lv, _html} = live(conn)

    lv
    |> form("#user-password-sign-in-with-password", %{
      "user" => %{
        "email" => "zach@example.com",
        "password" => "so-secure!"
      }
    })
    |> render_submit()

    assert_received {_ref, {:redirect, _topic, %{to: new_to}}}
    assert %{path: "/auth/user/password/sign_in_with_token"} = URI.parse(new_to)
  end

As you can see in support there are Example modules which represent example for use.
Also create action register_with_password on changeset is called but you will not find that create action in User module. I think it’s because it’s implicit in password authentication i.e. it’s not necessary to explicitly define the create action for that strategy.