Setting up custom response for exception in Phoenix Application

Question

im writing phoenix application with ecto and have the following snippet in the test

{:ok, data} = Poison.encode(%{email: "nonexisting@user.com", password: "mypass"})

conn()
|> put_req_header("content-type", "application/json")
|> put_req_header("accept", "application/json")
|> post(session_path(@endpoint, :create), data)
> json_response(:not_found) == %{}

this throws a Ecto.NoResultsError

i have this defined

defimpl Plug.Exception, for: Ecto.NoResultsError do
  def status(_exception), do: 404
end

but the test still throws Ecto.NoResultsError, Any pointers?

Answer 1

Let's consider how it works per environment.

• In :prod, the default is to render error pages, so you should see a page rendered by YourApp.ErrorView with the status code;

• In :dev, the default is to show debug pages, because the majority of times you have an error while building your code. If you want to see the actually rendered error page, you need to set debug_errors: false in your config/dev.exs;

• In :test, it works like production but, because you are calling your application from the test, your test will also crash if your application crashes. We are improving this on future versions, where you should be able to write something like:

  assert_raise Ecto.NoResultsError, fn ->
    get conn, "/foo"
  end
  {status, headers, body} = sent_response(conn)
  assert status == 404
  assert body =~ "oops"
  

Answer 2

Phoenix 1.1.0 introduced Phoenix.ConnTest.assert_error_sent/2 to make testing similar cases easier.

From the documentation:

Asserts an error was wrapped and sent with the given status.

Useful for testing actions that you expect raise an error and have the response wrapped in an HTTP status, with content usually rendered by your MyApp.ErrorView.

Usage example:

assert_error_sent :not_found, fn ->
  get conn(), "/users/not-found"
end

response = assert_error_sent 404, fn ->
  get conn(), "/users/not-found"
end
assert {404, [_h | _t], "Page not found"} = response