Testing Phoenix Controller rendering

Hi there!

I have a basic controller "welcome" that does: `render(conn, "index.html", profile: profile)`
There are some assigns to render

I want to write a test that demonstrates that the rendering is correct

if I do:

```elixir
conn = get(conn, "/welcome")
assert html_response(conn, 200) =~"hi"
```

Since some template assigns are present in the template, my test says that a key is not present.

Using `Plug.Conn.assign(conn, :profile, %{k: v})` is ineffective.

Does anyone know how to do this? The doc is void on this or didn't find where.