Assert a function output is less than or equal to an expression.
Pseudocode: function(a) ≤ b
use assertables::*; let a: i8 = -1; let b: i8 = 2; assert_fn_le_x!(i8::abs, a, b);
assert_fn_le_x
assert_fn_le_x_as_result
debug_assert_fn_le_x