At some point or another, most programmers find they need to compare floating-point numbers for equality. The typical idiom is to test if the absolute value of the difference of the numbers is within a desired tolerance, usually called epsilon. This module provides such a function for use with Test::Harness. Usage is similar to other test functions described in Test::More. Semantically, the delta_within function replaces this kind of construct:
ok ( abs($p - $q) < $epsilon, '$p is equal to $q' ) or
diag "$p is not equal to $q to within $epsilon";
While there's nothing wrong with that construct, it's painful to type it repeatedly in a test script. This module does the same thing with a single function call. The delta_ok function is similar, but either uses a global default value for epsilon or else calculates a 'relative' epsilon on the fly so that epsilon is scaled automatically to the size of the arguments to delta_ok. Both functions are exported automatically.
Because checking floating-point equality is not always reliable, it is not possible to check the 'equal to' boundary of 'less than or equal to epsilon'. Therefore, Test::Number::Delta only compares if the absolute value of the difference is less than epsilon (for equality tests) or greater than epsilon (for inequality tests).
