bn: Add simple test for mod_sqrt

        b.set_const_time();

        assert!(b.is_const_time())

    }

    #[cfg(ossl110)]

    #[test]

    fn test_mod_sqrt() {

        let mut ctx = BigNumContext::new().unwrap();

        let s = BigNum::from_hex_str("47A8DD7626B9908C80ACD7E0D3344D69").unwrap();

        let p = BigNum::from_hex_str("81EF47265B58BCE5").unwrap();

        let mut out = BigNum::new().unwrap();

        out.mod_sqrt(&s, &p, &mut ctx).unwrap();

        assert_eq!(out, BigNum::from_hex_str("7C6D179E19B97BDD").unwrap());

    }

}