Version 0.2.9 of the elixir_mock library now allows you to create mocks from erlang modules like :erlang and :inet.

test "should create simple mocks from erlang modules" do
    mock = mock_of :erlang
    assert mock.self() == nil
end

test "should create custom mocks from erlang modules" do
    with_mock(mock) = defmock_of :inet do
      def ip(_), do: :fake_ip
    end
    assert mock.ip(nil) == :fake_ip
end