Apply suggestions from code review

Co-authored-by: José Valim <[email protected]>

Author: QuinnWilton

lib/elixir/lib/protocol.ex

@@ -812,7 +812,7 @@ defmodule Protocol do
       # Without this, a protocol that defines no functions won't be detected
       # as a behaviour by the Erlang compiler, and any implementations of that
       # protocol will log a warning.
-      @callback __impl__(:foo) :: module()
+      @callback __impl__(:for) :: module()
       @callback __impl__(:target) :: module()
       @callback __impl__(:protocol) :: module()
     end

lib/elixir/test/elixir/protocol_test.exs

@@ -155,15 +155,11 @@ defmodule ProtocolTest do
   end
 
   test "protocol with no functions is a behaviour" do
-    refute capture_err(fn ->
-             Code.eval_string("""
-             defprotocol ProtoNoFunctions do
-             end
-
-             defimpl ProtoNoFunctions, for: Integer do
-             end
-             """)
-           end) =~ "module ProtoNoFunctions is not a behaviour"
+    defprotocol ProtoNoFunctions do
+    end
+
+    defimpl ProtoNoFunctions, for: Integer do
+    end
   end
 
   test "protocol defines functions and attributes" do