nalgebra::assert_approx_eq!

macro_rules! assert_approx_eq(
    ($given: expr, $expected: expr) => ({
        let (given_val, expected_val) = (&($given), &($expected));
        if !ApproxEq::approx_eq(given_val, expected_val) {
            panic!("assertion failed: `left ≈ right` (left: `{:?}`, right: `{:?}`, tolerance: `{:?}`)",
                *given_val, *expected_val,
                ApproxEq::approx_epsilon(Some(*given_val))
            )
        }
    })
);

Asserts approximate equality of two values with the ApproxEq trait.