Macro assert_near 

macro_rules! assert_near {
    ($x: expr, $y: expr, $delta: expr) => { ... };
}

Asserts that x and y are within delta of one another.

x and y must be of a common type that supports both subtraction and negation. (Note that it would be natural to define this macro using abs(), but when attempting to do so, the compiler fails to apply its inference rule for under-constrained types. See [https://github.com/rust-lang/reference/issues/104].)