Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

libs/test/doc/src/examples/example42.cpp

#define BOOST_TEST_MODULE example
#include <boost/test/included/unit_test.hpp>
#include <boost/test/floating_point_comparison.hpp>

//____________________________________________________________________________//

BOOST_AUTO_TEST_CASE( test )
{
    double v1 = 1.23456e-10;
    double v2 = 1.23457e-10;

    BOOST_CHECK_CLOSE( v1, v2, 0.0001 );
    // Absolute value of difference between these two values is 1e-15. They seems 
    // to be very close. But we want to checks that these values differ no more then 0.0001%
    // of their value. And this test will fail at tolerance supplied.
}

//____________________________________________________________________________//