webpack-karma-warnings-plugin.js

/*
 * This plugin makes sure karma doesn't run any specs when there's a
 * compilation error in a module by including a module even if the module has errors.
 *
 * Webpack's normal behaviour is to not include modules which have errors,
 * which causes Karma to run all the tests without the failed spec.
 *
 * Some links to where this magic actually happens in Webpack:
 *
 * The module will be removed from the dependency:
 * https://github.com/webpack/webpack/blob/v1.12.14/lib/Compilation.js#L646-L649
 *
 * and dependencies without a module won't be included in the module map:
 * https://github.com/webpack/webpack/blob/v1.12.14/lib/ContextModule.js#L87-L89
 *
 * Setting the module._source to a javascript error is copied from:
 * https://github.com/webpack/webpack/blob/v1.12.14/lib/NormalModule.js#L127
 */
var WebpackKarmaWarningsPlugin = function() {};
var RawSource = require("webpack-core/lib/RawSource");

WebpackKarmaWarningsPlugin.prototype.apply = function(compiler) {
  compiler.plugin("compilation", function(compilation) {
    compilation.plugin("failed-module", function(module) {
      var moduleErrorMessage = module.error.error.toString()
      module._source = new RawSource(`throw new Error(${JSON.stringify(moduleErrorMessage)});`);
      module.error = null;
    });
  });
};

module.exports = WebpackKarmaWarningsPlugin;

for those looking for a webpack 4 approach in typescript - https://gist.github.com/jonesmac/9ef456153c714db56be0ec24b61c6fbb

I found I had to use the compilation.warnings.length to test if a relevant error occurred. I tried the failedModule hook but with no success.