Angular unit testing - ignore stylesheets

Question

I'm trying to speed up the unit tests for a fairly large non-cli Angular application and had a thought: what if I skipped the style sheets? The slowest step in running the tests (by a wide margin) is Webpack compiling the thousands of scss style sheets contained in the app.

I've changed the webpack settings to load empty modules for these files:

 { test: /\.css$/, use: 'null-loader' },
 { test: /\.scss$/, use: 'null-loader' },

But of course the Angular testbed's metadata-resolver now complains about the modules being empty..

 Error: Expected 'styles' to be an array of strings.
      at assertArrayOfStrings (webpack:///node_modules/@angular/compiler/esm5/compiler.js:2522 <- config/spec-bundle.js:109446:19)
      at CompileMetadataResolver.getNonNormalizedDirectiveMetadata (webpack:///node_modules/@angular/compiler/esm5/compiler.js:14965 <- config/spec-bundle.js:121889:13)

I think what I need to do here is to either load every style sheet as an empty string, or set the Testbed up in such a way that it ignores references to .scss files in the component metadata.

Is there a way to accomplish one of these solutions, or is there perhaps a smarter way of going about this?

Answer 1

I solved it!

By creating a custom loader that loads all .scss-files as empty strings I can drastically reduce the time it takes to compile my unit tests.

ignore-sass-loader.js:

const sass = require("node-sass");
const async = require("neo-async"); const threadPoolSize = process.env.UV_THREADPOOL_SIZE || 4;
const asyncSassJobQueue = async.queue(sass.render, threadPoolSize - 1);

module.exports = function ignoreSassLoader(content) { 
    const callback = this.async(); 

    asyncSassJobQueue.push({}, () => { 
        callback(null, ' '.toString(), null); 
    }); 
};

This is then resolved by adding an alias to the webpack configuration:

module.exports = function () {
    return {
               resolveLoader: {
                   alias: {
                       'ignore-sass-loader': resolve(__dirname, '../config/loaders/ignore-sass-loader')
                   }
               },

And then finally I use my loader together with the raw-loader:

{
     test: /\.scss$/,
     use: ['raw-loader', 'ignore-sass-loader'],
},