[Proposal] Contextual data in ExUnit.assert/1 or assert/2

[Derek Wiers]

So, we have the assert/1 macro in ExUnit, which does a really nice job of pointing out actual failures - a diff, etc, depending on what you give it. We also have assert/2, a function where you can insert your own message. I propose that we have perhaps another option: a variant of assert(assertion, contextual_data: %{foo: "bar"}). Basically, I love that diffing we do in assert/1, and just want to append some relevant data to the message, which is particularly helpful if I'm running an assertion in a loop (think poor man's property-based testing) with different data -- the line number isn't going to allow me enough data to figure out what exactly just failed.

I understand it wouldn't be trivial to do, pretty much because there's already an assert/2 with opts and with message, and they're functions not macros...

Sorry if I'm missing anything about proposals - this is my first one!

I'm willing to maybe put some time into a PR here, if the feedback is positive and has a bit of guidance (Elixir is my day-job, so I do have some experience)

Thanks,

Derek

[Ben Wilson]

+1 to this from me. We have a variety of asserts inside of a list that always have commented out dbg statements above them to help with failures. Passing those into assert would be great.

[Jason Axelson]

Big +1 from me as well. I often skip using `assert/2` because of the need to re-implement the rich diffing logic that `assert/1` gives. Generally I only truly want to provide additional context that will help the developer understand what failed rather than wanting my own "diffing" output.

-Jason

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[Jon Rowe]

+1 here, more context is often useful but the diff support is crucial.

Cheers

Jon

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[José Valim]

If someone would like to tackle this, please go ahead. I assume it will require a reasonable amount of work.

José Valim

https://dashbit.co/

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