message: Derive: add a test for empty tuple struct
diff: @@ -31,6 +31,9 @@ struct U;
  #[derive(H5Type)]
  struct T(i64, pub u64);
  +#[derive(H5Type)]
  +struct T0();
  +
  #[test]
  fn test_compound_unit() {
  assert_eq!(U::type_descriptor(),
  @@ -38,6 +41,7 @@ fn test_compound_unit() {
  fields: vec![],
  size: 0,
  }));
  + assert_eq!(U::type_descriptor(), T0::type_descriptor());
  }
  #[test]
  