webpack-karma-warnings-plugin.ts

/*
 * This plugin makes sure karma doesn't run any specs when there's a
 * compilation error in a module by checking the finished compilation for warnings
 * which would prevent tests from accurately running.
 *
 * Inspiration for looking at the warnings length
 * https://gist.github.com/Stuk/6b574049435df532e905
 */
import { Compiler } from 'webpack';

export class WebpackKarmaWarningsPlugin {
  public apply(compiler: Compiler) {
    compiler.hooks.emit.tapAsync(
      'WebpackKarmaWarningsPlugin',
      (compilation, callback) => {
        if (compilation.warnings.length) {
          throw new Error(compilation.warnings.toString());
        }
        callback();
      }
    );
  }
}

This no longer works with Webpack 5 😭