write first test and let changeset errors return error json in controller

lib/entendu_web/views/changeset_view.ex

@@ -0,0 +1,15 @@
+defmodule EntenduWeb.ChangesetView do
+  use EntenduWeb, :view
+
+  def translate_errors(%Ecto.Changeset{} = changeset) do
+    Ecto.Changeset.traverse_errors(changeset, &translate_error/1)
+  end
+
+  def translate_errors(errors = %{}), do: errors
+
+  def render("error.json", %{changeset: changeset}) do
+    # When encoded, the changeset returns its errors
+    # as a JSON object. So we just pass it forward.
+    %{errors: translate_errors(changeset)}
+  end
+end