Executable documentation

by Taylor Fausak on

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Back in 1999, Tim Peters released doctest for Python. His motivation was simple:

  • Examples are priceless.
  • Examples that don’t work are worse than worthless.
  • Examples that work eventually turn into examples that don’t.

Recently, I’ve been working on many small side projects. I found myself with the same motivation as Mr. Peters. Since most of my projects were written in Ruby, I looked for a doctest gem. Unfortunately I didn’t like what I found.

From what I can tell, rubydoctest is the de facto standard. It doesn’t appear to be actively maintained, and it has a couple glaring omissions, like ellipsis wildcards and expected exceptions. I considered forking it to fix these issues, but ultimately decided to create my own gem instead.

This made sense to me because my aims are slightly different. I want a tool that can be used to write doctests, but it should also support a kind of literate programming. In particular, I should be able to feed it a project’s README.md and it should run that as a test. This is inspired by Simon Hengel’s tool markdown-unlit.

My own tool, Erudite, isn’t as robust as either rubydoctest or markdown-unlit yet. Even so, it’s be useful for testing. I can fire up the executable and paste in code from a README.md. It’ll do all the work to determine if that code is valid or not.

$ bundle exec erudite
>> require 'stoplight'
=> true
>> Stoplight.data_store
=> #<Stoplight::DataStore::Memory:0x... @data={}>

I’m looking forward to rounding out Erudite’s feature set, and I hope you find it useful. Check out its project page or the source on GitHub