TEST(StrTest, Convert) {
  EXPECT_EQ("42", str(42));
  std::string s = str(Date(2012, 12, 9));
  EXPECT_EQ("2012-12-9", s);
}
TEST(StrTest, Convert) {
  EXPECT_EQ("42", str(42));
  std::string s = str(Date(2012, 12, 9));
  EXPECT_EQ("2012-12-9", s);
}