Fix all tests 🎉

Author: Leo B

lib/ecto/association.ex

@@ -249,6 +249,9 @@ defmodule Ecto.Association do
     values = List.wrap(values)
 
     query = case {join_to, dest_out_key, values} do
+      {nil, single_key, [single_value]} when is_atom(single_key) and not is_list(single_value) ->
+        query
+        |> where([{dest, final_bind}], field(dest, ^single_key) == ^single_value)
       {nil, [single_key], [single_value]} ->
         query
         |> where([{dest, final_bind}], field(dest, ^single_key) == ^single_value)

lib/ecto/changeset.ex

@@ -3792,7 +3792,8 @@ defmodule Ecto.Changeset do
     |> merge_related_keys(changes, types, msg_func, &traverse_validations/2)
   end
 
-  defp atom_concat(atoms) do
+  defp atom_concat(atom) when is_atom(atom), do: Atom.to_string(atom)
+  defp atom_concat(atoms) when is_list(atoms) do
     atoms
     |> Enum.map(&Atom.to_string/1)
     |> Enum.join("_")