[Boost-users] Boost.Test: floating point comparison using absolute diference

[Georgios Sermaidis via Boost-users]

Hi all,

I am trying to find a way to make the boost unit test framework use an absolute difference for floating point comparison instead of the relative difference. 

I searched the documentation to try to find a suitable decorator but couldn’t find anything. Any help is much appreciated!

#define BOOST_TEST_MODULE example
#include <boost/test/included/unit_test.hpp>
// boost::unit_test::tolerance uses relative difference and hence this test will pass; 
// is there anything I can use here to indicate absolute difference?
BOOST_AUTO_TEST_CASE(my_test, * boost::unit_test::tolerance(0.1) ) 
{
  BOOST_TEST(10.1 == 10.3);
}

[Raffi Enficiaud via Boost-users]

Le 29.12.17 à 17:33, Georgios Sermaidis via Boost-users a écrit :

> Hi all,
>
> I am trying to find a way to make the boost unit test framework use an
> absolute difference for floating point comparison instead of the
> relative difference. 
> I searched the documentation to try to find a suitable decorator but
> couldn’t find anything. Any help is much appreciated!
>
> #defineBOOST_TEST_MODULEexample
>
> #include<boost/test/included/unit_test.hpp>
>
>

> //boost::unit_test::toleranceusesrelativedifference and hence this test

> will pass; 
>
> // isthereanythingIcanusehereto indicateabsolutedifference?
>
> BOOST_AUTO_TEST_CASE(my_test,*boost::unit_test::tolerance(0.1))
>
> {
>
>
> BOOST_TEST(10.1==10.3);
>
> }

What you want to do is discussed here in the doc:
http://www.boost.org/doc/libs/1_66_0/libs/test/doc/html/boost_test/testing_tools/extended_comparison/floating_point/floating_points_comparison_impl.html

You may just use

BOOST_TEST(left - right == .0, boost::unit_test::tolerance(0.1));

and I think it should use absolute tolerance on the absolute value of
left-right.

If nothing works, there is always the good old comparison:
BOOST_TEST((std::abs(left - right) < 0.1))

Note the double parenthesis, in this case BOOST_TEST will see only the
evaluation of the expression inside, which is cast to bool (less
elegant, but should work as last resort).

Raffi

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[Georgios Sermaidis via Boost-users]

Thank you. Is there a way to achieve this when comparing collections, i.e. when using boost::test_tools::per_element()?

[Raffi Enficiaud via Boost-users]

Le 30.12.17 à 14:41, Georgios Sermaidis via Boost-users a écrit :

> Thank you. Is there a way to achieve this when comparing collections,
> i.e. when using boost::test_tools::per_element()?
>
>
>> On 29 Dec 2017, at 19:37, Raffi Enficiaud via Boost-users

Apart from creating a collection of differences that you compare with a
collection of zeros (that can be wrap up in helper functions), I do not
see a way to use this facility as is. Looping over the elements would
certainly be the most maintainable and easy to understand choice.

[Georgios Sermaidis via Boost-users]

Got it, thank you so much

Regards,
Georgios