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```
```/// Macro to test that two values are approximately equal. It checks that the relative difference between
/// the two values is less than some epsilon value.
///
/// ```ignore
/// use approx_eq::assert_approx_eq;
/// fn main() {
///   assert_approx_eq!(1., 0.99999999999); // should pass
///   assert_approx_eq!(1., 0.99999999999, 1e-5); // should pass
///   assert_approx_eq!(1., 0.99999999999, 1e-20); // should fail
///   assert_approx_eq!(1., 2.) // should fail
/// }
/// ```

#[macro_use]
pub mod approx_eq {
#[macro_export]
/// Epsilon takes a default value of 1e-6.
/// It is also possible to specify the error level to use.
macro_rules! assert_approx_eq {
(\$x: expr, \$y: expr) => {
let eps = 1e-6;
let (x, y): (f64, f64) = (\$x, \$y);
assert!(&x.signum() == &y.signum());
let (x, y): (f64, f64) = (x.abs(), y.abs());
assert!((&x - &y).abs() / [x, y].iter().cloned().fold(f64::NAN, f64::min) < eps);
};
(\$x: expr, \$y: expr, \$e: expr) => {
let (x, y): (f64, f64) = (\$x, \$y);
assert!(&x.signum() == &y.signum());
let (x, y): (f64, f64) = (x.abs(), y.abs());
assert!((&x - &y).abs() / [x, y].iter().cloned().fold(f64::NAN, f64::min) < \$e);
};
}
}

#[test]
fn test_noeps() {
assert_approx_eq!(1., 1.);
assert_approx_eq!(1., 1.000001);
}

#[test]
fn test_witheps() {
assert_approx_eq!(1.0000000001, 1., 1e-5);
}

#[test]
#[should_panic(expected = "assertion failed")]
fn test_invalid() {
assert_approx_eq!(1.0000000001, 1., 1e-10);
}

#[test]
#[should_panic(expected = "assertion failed")]
fn test_sign() {
assert_approx_eq!(1., -1.);
}
```