     end
   end
 
-  describe ".handle_call :prev" do
+  describe "GameServer.handle_call(:prev, _, _)" do
     test "does nothing when the server is stopped" do
       assert(GameServer.handle_call(:prev, self(), @halt_state) ==
         {:reply, :ok, @halt_state})

    end
  end

  describe ".step_back" do
    test "does nothing when the history is empty" do
      assert GameServer.step_back(@empty_state) == @empty_state
    end

    end
  end

  describe "GameServer.handle_call(:next, _, _)" do
    test "executes the reducer once if the game is not ended" do
      state = %State{world: 1, reducer: &(&1+1)}

