Since Rust 1.28.0, unit tests can return Result. In other words, you can use ? on unit tests’ functions.

But, while working on my pull request to use that on solana, I have found 2 pitfalls.

left is 1, right is 0?

Sadly the error message regarding a failing unit test is not great.

thread '...' panicked at 'assertion failed: `(left == right)`
  left: `1`,
 right: `0`', libtest/

There is an open pull request to address the issue. So it will be fixed at 1.30, according to #48854.

The backtrace doesn’t include the line number of ?

Thils is probably hard to address. Due to the way it uses Result, libtest, the test runnner can’t tell where the failing ? is. The pull request on solana had the discusstion about that, and eventually we settled that it would be okay. But it may be frustrating if you have multiple ?s in a long function. We shouldn’t have such a function though.

It actually reminds me Go’s errors. They are not having stracktraces by default and companies like Dropbox implement its own variants to have them. Would Result<T, E> have something similar since nice ? syntax pushes people to use more Results? I am not so sure.