Using snapshots for testing

[nyurik]

Hi, thx for maintaining this. I wonder if the insta snapshots can be used for testing?

#[test]
fn my_test() {
  let input: TokenStream = quote!( ... );
  let result = my_code_generator(input).unwrap();

  // running insta bless will update "" to the actual value, assuming result has Display
  assert_snapshot!(result, @"");
}

It seems syn crate uses exactly the same approach, but I have no idea how to get started with using it in my code. Thx!