These tools are used to check that supplied values is small enough. The "smallness" is defined by absolute value of the tolerance supplied as a second argument. Note that to use these tools you need to include additional header floating_point_comparison.hpp. Use these tools with caution. To compare to values on closeness it's preferable to use BOOST_<level>_CLOSE tools.
The first parameter is the value to check. The second parameter is the tolerance .
int test_main( int, char* [] ) { double v = -1.23456e-3; BOOST_CHECK_SMALL( v, 0.000001 ); return 0; }
test.cpp(4) : error in test_main: absolute value of v{1.23456e-3} exeeds 1e-06