Writing Tests for Plugin-Postcss: Mocking?

[thescripted]

This may be a naive question, but I believe it would be useful to add a stub postcss config file to run and test this block:

https://github.com/pikapkg/snowpack/blob/f563593a2511573b1a9962afe4fcef34c91dff4c/plugins/plugin-postcss/plugin.js#L7-L11

I'm not entirely sure how to mock imported plugins. (i.e., if cssnano is in the postcss config, then the snapshot output should be a minified css file). Is there any advice on how to do this, if this is the right track?

[drwpow]

Not a naïve question at all! This actually seems difficult, especially since we’re running the CLI command postcss. There’s not really a way that I can think of off the top of my head to mock only cssnano, since that’s loaded by the CLI.

But I think we could mock execa like so (Jest pseudocode):

const postcss = require('postcss');
jest.mock('execa', () => (command) => {
  postcss(/* do some custom config here for testing */)
}));

const plugin = import ('./plugin.js'); // make sure this comes after `jest.mock`!

It’s a bit involved, but we could basically load our own PostCSS everything by mocking execa.

If this totally wasn’t what you were asking, forgive me!

[FredKSchott]

There are some examples of this on our other tests as well, if you look around. And I know @gr2m wanted to take a stab at writing a "plugin example repo" github template.