Add coverage as a separate babel loader if loaders already exist

scripts/run-e2e-tests.mjs

@@ -181,17 +181,22 @@ async function npmInstall(cwd, prefix) {
  */
 async function setupTests(projectPath, prefix) {
 	const name = path.basename(projectPath);
-	const log = (...msgs) => console.log(`${info(prefix)}`, ...msgs);
+	const log = (...msgs) => console.log(info(prefix), ...msgs);
+	const throwError = (...msgs) => {
+		process.exitCode = 1;
+		console.error(error(prefix), ...msgs.map((msg) => error(msg)));
+		throw new Error(msgs[0]);
+	};
 
 	log(`Beginning E2E test at`, projectPath);
 	const pkgJsonPath = path.join(projectPath, 'package.json');
 	if (!(await fileExists(pkgJsonPath))) {
 		prefix = error(prefix);
-		console.error(
-			`${prefix} Could not locate package.json for "${name}". Ensure every e2e test has a package.json defined.`
+		throwError(
+			`Could not locate package.json for "${name}".`,
+			`Ensure every e2e test has a package.json.\n`,
+			`${prefix} Expected to find one at "${pkgJsonPath}".`
 		);
-		console.error(`${prefix} Expected to find one at "${pkgJsonPath}".`);
-		throw new Error(`Could not locate package.json for "${name}".`);
 	}
 
 	const pkg = JSON.parse(await fs.readFile(pkgJsonPath, 'utf8'));
@@ -228,10 +233,22 @@ async function setupTests(projectPath, prefix) {
 			await onExit(cp);
 		} catch (e) {
 			process.exitCode = 1;
-			console.error(error(prefix) + ` Test run failed: ${e.message}`);
+			throwError(`Test run failed: ${e.message}`);
 		}
 
-		// TODO: validate coverage/lcov.info is not empty
+		const coveragePath = path.join(projectPath, 'coverage', 'lcov.info');
+		if (!(await fileExists)) {
+			throwError(
+				`Code coverage failed to generate results: Results file does not exist at ${coveragePath}`
+			);
+		}
+
+		const coverageInfo = await fs.readFile(coveragePath, { encoding: 'utf8' });
+		if (!coverageInfo) {
+			throwError(
+				`Code coverage failed to generate results: Results file is empty`
+			);
+		}
 	};
 }
 

src/lib/babel-loader.js

@@ -1,4 +1,15 @@
-export default function babelLoader(options) {
+export function getCoverageBabelLoader() {
+	return {
+		test: /\.jsx?$/,
+		exclude: /node_modules/,
+		loader: require.resolve('babel-loader'),
+		query: {
+			plugins: [require.resolve('babel-plugin-istanbul')],
+		},
+	};
+}
+
+export function getDefaultBabelLoader(options) {
 	return {
 		test: /\.jsx?$/,
 		exclude: /node_modules/,

src/webpack.js

@@ -1,7 +1,10 @@
 import path from 'path';
 import delve from 'dlv';
 import { tryRequire, dedupe } from './lib/util';
-import babelLoader from './lib/babel-loader';
+import {
+	getDefaultBabelLoader,
+	getCoverageBabelLoader,
+} from './lib/babel-loader';
 import cssLoader from './lib/css-loader';
 
 /**
@@ -104,6 +107,21 @@ export function addWebpackConfig(karmaConfig, pkg, options) {
 		return Object.assign({}, configured || {}, value);
 	}
 
+	let existingBabelLoader = getLoader((rule) =>
+		`${rule.use},${rule.loader}`.match(/\bbabel-loader\b/)
+	);
+	if (existingBabelLoader) {
+		if (options.coverage) {
+			loaders.push(getCoverageBabelLoader());
+		}
+	} else {
+		loaders.push(getDefaultBabelLoader(options));
+	}
+
+	if (!getLoader('foo.css')) {
+		loaders.push(cssLoader(options));
+	}
+
 	for (let prop of Object.keys(karmaConfig.preprocessors)) {
 		karmaConfig.preprocessors[prop].unshift('webpack');
 	}
@@ -115,21 +133,7 @@ export function addWebpackConfig(karmaConfig, pkg, options) {
 		// devtool: 'module-source-map',
 		mode: webpackConfig.mode || 'development',
 		module: {
-			// @TODO check webpack version and use loaders VS rules as the key here appropriately:
-			//
-			// TODO: Consider adding coverage as a separate babel-loader so that
-			// regardless if the user provides their own babel plugins, coverage still
-			// works
-			rules: loaders
-				.concat(
-					!getLoader((rule) =>
-						`${rule.use},${rule.loader}`.match(/\bbabel-loader\b/)
-					)
-						? babelLoader(options)
-						: false,
-					!getLoader('foo.css') && cssLoader(options)
-				)
-				.filter(Boolean),
+			rules: loaders,
 		},
 		resolve: webpackProp('resolve', {
 			modules: webpackProp('resolve.modules', [