Replace assert! macros with macros from approx crate

[stefan-k]

Currently most assertions in the argmin-math tests use the assert! macro, which is somewhat inconvenient for comparing floats. It would be great if those were replaced with the assert macros of the approx crate.

Status

• primitives (Replace assert! macros with macros from approx crate #327)
• vec (Replace assert! macros with macros from approx crate #327)
• ndarray (Use assert_relative_eq! macros in ndarray and nalgebra backend tests #404)
• nalgebra (Use assert_relative_eq! macros in ndarray and nalgebra backend tests #404)

[rpopplewell]

So for the sake of clarity we're looking for this sort of change for all tests hit by cargo test -p argmin-math right?

// Old
// assert!(((a as $t - res.re) as f64).abs() < std::f64::EPSILON);
// assert!(((-b as $t - res.im) as f64).abs() < std::f64::EPSILON);

// New
assert_relative_eq!(a as f64, res.re as f64, epsilon = std::f64::EPSILON);
assert_relative_eq!(-b as f64, res.im as f64, epsilon = std::f64::EPSILON);

[stefan-k]

Yes, this is correct! :)