Writing a good MWE

A Minimal Working Example is the single most effective way to get help with a bug or to report one. A good MWE lets someone else reproduce your problem on the first try, without asking follow-up questions.

MinimalWorkingExamples.jl takes care of running the code and generating Markdown ready to paste into a GitHub issue, Discourse post, or Slack. What it can't do for you is decide what code to include. These tips cover that part.

Make it minimal

Strip away everything that isn't needed to trigger the behaviour.

• Only keep code that is necessary to reproduce the problem. If removing a line changes nothing, remove it.
• Shrink the data. A bug that shows up on a 10,000-row table could probably be reduced to 10 rows.
• Use built-in or generated data (rand, 1:5) instead of files on your disk.

Minimal is not just polite: shrinking the example is often how you find the cause yourself.

Make it self-contained

Therefore, your snippet must:

• Include every using/import the code needs. Packages are automatically installed from using/import statements.
• Don't reference variables, functions, or constants that are defined elsewhere in your session but not in the snippet.

Make it reproducible

You want the reader to get the same result you did.

• Seed any randomness if it affects the result (using Random; Random.seed!(1405)), so the output is deterministic.
• If the behaviour is version-specific, pin the packages with packagespecs, or attach a full environment with manifest_path (see Reproducing an exact environment). You can also set manifest=true to include the manifest in a collapsible details section of the generated Markdown.

Make the problem obvious

• Arrange the code so the final expression is the surprising part, e.g. a wrong value or an error.
• If the result merely looks wrong, say what you expected in the surrounding text.

Further reading

• How to make a great R reproducible example — language-agnostic advice that applies just as well to Julia.