triangle: incorrect test in some tracks

[kytrinyx]

Please check if there's a test that states that a triangle with sides 2, 4, 2 is invalid. The triangle inequality states that for any triangle, the sum of the lengths of any two sides must be greater than or equal to the length of the remaining side. If this doesn't affect this track, go ahead and just close the issue.

[kytrinyx]

There was a bit of confusion with this issue. I've summarized my current understanding here: exercism/problem-specifications#202

I am closing this issue. If necessary I will open a new issue once we have come to an agreement about how to resolve the inconsistencies and what exact steps to take.

[LegalizeAdulthood]

For C++ we can address this by changing this test case to avoid the strict equality:

BOOST_AUTO_TEST_CASE(medium_triangles_violating_triangle_inequality_are_illegal)
{
    BOOST_REQUIRE_THROW(triangle::kind(2, 4, 2), std::domain_error);
}

[kytrinyx]

The problem here is the subtle difference between violating the triangle inequality, and not violating it but being degenerate. 2, 4, 2 doesn't violate the basic triangle inequality.

[LegalizeAdulthood]

The test is reporting it as a violation (throwing std::domain_error exception)

[kytrinyx]

Right, according to the triangle inequality, 2, 4, 2 is not in violation (it just specifies a degenerate triangle).

I think that it would be easier to avoid the exact edge case and use 5, 5, 11 as the input, which clearly violates the inequality.