CSV with iterable of elements creates only 2 lines (header+content)

[woshilapin]

Description

I believe this playground explains the problem. When we .serialize() a Vec of objects that implements Serialize with the Serializer of the csv crate, it doesn't create a line for each object but flatten them together. There might be good reasons to do it in csv but it does make assert_csv_snapshot!() not really useful. I hope I did not miss an obvious solution to what I'm trying to do. And also, I was not sure to report this as a bug or as a feature so please forgive me if that's not the right category.

Additional helpful information:

• Version of insta: 1.5.2
• Version of rustc: 1.49.0
• Operating system and version: Linux Ubuntu 20.10

What did you expect

I would expect to be able to send a Vec or any kind of iterator of objects implementing Serialize, to the macro assert_csv_snapshot!() and be able to have a multiline *.snap instead of a 2-lines (one header line + one content line).

[mitsuhiko]

Yep. I also ran into this and I think the current format is not particularly useful. Would accept a PR to modify this behavior but currently relatively low priority for myself to fix this.

[woshilapin]

I wanted to be sure that it could not be solved at a higher level, but I would say that BurntSushi/rust-csv#221 is a pretty clear answer about it.

I might take a look at how to improve the behavior of assert_csv_snapshot!().

[woshilapin]

Thank you for the feature! That is just perfect!