Clippy complaining on strict f32 comparison

Question

I have a test assertion that looks like this

assert_eq!(-0.000031989493, res);

which works for the test. But when I run Clippy on my test it complains.

error: strict comparison of `f32` or `f64`
   --> src/main.rs:351:9
    |
351 |         assert_eq!(-0.000031989493, res);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `f32::EPSILON` and `f64::EPSILON` are available for the `error_margin`
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#float_cmp
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

I've looked at the provided link https://rust-lang.github.io/rust-clippy/master/index.html#float_cmp and rewrote it like this instead.

assert_eq!(
    true,
    (res - -0.000031989493).abs() < f32::EPSILON
);

But that makes the test less readable and if the test fails I can't see the result of what I'm testing in the output.

How should I write my f32 comparison assertions so that Clippy is happy and so that the tests still output the values in the terminal if it fails?

Or should I just not run Clippy on my tests?

Thanks!

Answer 1

Ok so I've copied and altered the assert_eq macro a bit

macro_rules! assert_almost_eq {
    ($left:expr, $right:expr, $prec:expr) => {{
        match (&$left, &$right) {
            (left_val, right_val) => {
                let diff = (left_val - right_val).abs();

                if diff > $prec {
                    panic!(
                        "assertion failed: `(left == right)`\n      left: `{:?}`,\n     right: `{:?}`",
                        &*left_val, &*right_val
                    )
                }
            }
        }
    }};
}

I don't really understand everything, like the reason for the match, but it seems to solve my problem.