[boost] Unit test could usefully output more significant digits to log files?

From: Paul A Bristow (pbristow_at_[hidden])
Date: 2004-07-26 12:33:18

In setting up a test for math function accuracy, I incorrectly coded thus:

  BOOST_CHECK_EQUAL(sin(0.5), 0.479426);

and got the somewhat puzzling - apparently wrong - message

error in "call_test_main": test sin(0.5) == 0.479426 failed [0.479426 !=
0.479426]

On most days of the week, one would expect [0.479426 == 0.479426]!

I should of course have written

  BOOST_CHECK_EQUAL(sin(0.5), 0.47942553860420301);

(or used 

  BOOST_CHECK_CLOSE(sin(0.5), 0.47942553860420301, 1e-16);)

But I wonder if the test program would be even more helpful if it output all
possibly significant digits.

In test_tools.hpp, I have added an increase to the ostream precision
(default only 6 digits) int print_log_value thus

  template<typename T>
  struct print_log_value {
  void    operator()( std::ostream& ostr, T const& t )
  {
    if(std::numeric_limits<T>::is_specialized &&
std::numeric_limits<T>::radix == 2)
    { // Show all possibly significant digits (for example, 17 for 64-bit
double).
      ostr.precision(2 + std::numeric_limits<T>::digits * 301/1000);
    }
    ostr << t; // by default print the value.
  }
};

so that the message is no longer 

 test sin(0.5) == 0.479426 failed [0.47942553860420301 !=
0.47942600000000002]

and my folly obvious.

And after the original mistake is corrected

  BOOST_CHECK_EQUAL(sin(0.5), 0.47942553860420301);

The log file reports:

 info: sin(0.5) == 0.47942553860420301 passed.

Paul

PS (It does not appear to possible to change the precision 'externally' by
calling

cout.precision(17);

myTestLog.precision(17);

probably because ostr in test is contructed with default precision).

Paul A Bristow
Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB
[phone]  [phone]
mailto: pbristow_at_[hidden]