Great compiler messages? Great test failure messages!

I wrote a blog post on how to make great test failure messages for elm-test. I hope you find it interesting and useful :slight_smile:

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Very helpful post! I like the tip about using ANSI color codes in error messages, too, I hadn’t considered that. Great stuff!

Another trick that I find helpful is that the Red step in Test-Driven Development is to get the specific error message you want to see. If you see Red, but it’s

  • Not Red for the reason you intended, or
  • Not Red with a useful error message that tells you how to fix it

Then you’re not done with the red step yet. That little habit helps out a lot, because otherwise it’s easy to move on and end up with unhelpful error messages that get buried in the Green state.

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One thing to note about the ANSI color codes is that they’ll be in effect even if the user runs elm-test --no-color, and they’ll show up as “garbage” for elm-test --report json or elm-test --report junit. elm-test could strip the ANSI codes in those cases, I guess, but currently it doesn’t.

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