Dev: Fix coverage

Closes #471.

README.md

@@ -1,5 +1,6 @@
 [![NPM version](https://img.shields.io/npm/v/livepack.svg)](https://www.npmjs.com/package/livepack)
 [![Build Status](https://img.shields.io/github/actions/workflow/status/overlookmotel/livepack/test.yml?branch=master)](https://github.com/overlookmotel/livepack/actions)
+[![Coverage Status](https://img.shields.io/coveralls/overlookmotel/livepack/master.svg)](https://coveralls.io/r/overlookmotel/livepack)
 
 # Serialize live running code to Javascript
 

jest.config.js

@@ -9,7 +9,7 @@
 
 module.exports = {
 	testEnvironment: 'node',
-	runner: 'jest-light-runner',
+	runner: '<rootDir>/test/support/runner.mjs',
 	coverageDirectory: 'coverage',
 	coverageProvider: 'v8',
 	collectCoverageFrom: ['*.js', '!.eslintrc.js', '!jest.config.js', 'lib/**/*.js'],

package.json

@@ -68,12 +68,14 @@
     "@overlookmotel/eslint-config-jest": "^6.0.1",
     "@overlookmotel/eslint-config-node": "^4.1.0",
     "@overlookmotel/jest-extended": "^3.2.0",
+    "collect-v8-coverage": "^1.0.1",
     "eslint": "^8.30.0",
     "expect": "^29.3.1",
     "jest": "^29.3.1",
     "jest-expect-arguments": "^1.0.0",
     "jest-light-runner": "^0.4.1",
     "jest-matcher-utils": "^29.3.1",
+    "jest-util": "^29.3.1",
     "npm-run-all": "^4.1.5"
   },
   "keywords": [

test/support/coverage.js

@@ -0,0 +1,109 @@
+/* --------------------
+ * livepack
+ * Capture V8 coverage
+ * ------------------*/
+
+/* eslint-disable import/order, import/newline-after-import */
+
+'use strict';
+
+// Use internal module cache because some of same modules (e.g. `pirates`)
+// are also used by `register.js`. This avoids loading them twice.
+const {
+	useInternalModuleCache, useGlobalModuleCache, usingInternalModuleCache
+} = require('../../lib/shared/moduleCache.js');
+useInternalModuleCache();
+
+// Modules
+const {join: pathJoin, relative: relativePath} = require('path'),
+	{fileURLToPath} = require('url'),
+	{CoverageInstrumenter} = require('collect-v8-coverage'),
+	{globsToMatcher, replacePathSepForGlob} = require('jest-util'),
+	{addHook} = require('pirates'),
+	EXTS = require('@babel/core').DEFAULT_EXTENSIONS;
+
+// Imports
+const {collectCoverageFrom} = require('../../jest.config.js');
+
+useGlobalModuleCache();
+
+// Constants
+const TESTS_DIR = pathJoin(__dirname, '../'),
+	ROOT_DIR = pathJoin(TESTS_DIR, '../');
+
+// Exports
+
+module.exports = startCoverage;
+startCoverage.applyAfterAllHook = applyAfterAllHook;
+
+let instrumenter;
+
+/**
+ * Run by `jest-light-runner` before `./register.js`.
+ * Then run again in `afterAll` hook at end of each test file.
+ * Start capturing V8 coverage.
+ * @async
+ * @returns {undefined}
+ */
+async function startCoverage() {
+	instrumenter = new CoverageInstrumenter();
+	await instrumenter.startInstrumenting();
+}
+
+/**
+ * Register `afterAll` test hook to record V8 coverage data to `global.__coverage__`.
+ * `jest-light-runner` collects this and records it in the test result object as Babel coverage data.
+ * Custom runner `./runner.mjs` then moves it to the `.v8Coverage` property of result object.
+ *
+ * Code to call this function is added to bottom of every test file by pirates hook below.
+ *
+ * V8 coverage data is filtered to only files being assessed for coverage.
+ * This is done here rather than in the custom runner to minimise data transfer between
+ * worker thread running the test and the runner main thread.
+ *
+ * @returns {undefined}
+ */
+function applyAfterAllHook() {
+	afterAll(async () => {
+		// Record coverage data
+		global.__coverage__ = filterCoverageData(await instrumenter.stopInstrumenting());
+
+		// Start coverage inspector again for next test file
+		startCoverage(true);
+	});
+}
+
+/**
+ * Filter coverage data to files being monitored for coverage only.
+ * Based on:
+ * https://github.com/facebook/jest/blob/fb2de8a10f8e808b080af67aa771f67b5ea537ce/packages/jest-runtime/src/index.ts#L1217
+ *
+ * @param {Array<Object>} coverage - Coverage data captured by V8
+ * @returns {Array<Object>|undefined} - Conformed coverage data
+ */
+function filterCoverageData(coverage) {
+	if (collectCoverageFrom && collectCoverageFrom.length === 0) return undefined;
+
+	const filenameMatcher = globsToMatcher(collectCoverageFrom);
+
+	coverage = coverage
+		.filter(res => res.url.startsWith('file://'))
+		.map(res => ({...res, url: fileURLToPath(res.url)}))
+		.filter(
+			res => res.url.startsWith(ROOT_DIR)
+				&& filenameMatcher(replacePathSepForGlob(relativePath(ROOT_DIR, res.url)))
+		)
+		.map(result => ({result}));
+
+	return coverage.length > 0 ? coverage : undefined;
+}
+
+// Install extra require hook to add code to end of test files to install `afterAll` hook.
+addHook(
+	(code, path) => (
+		(!usingInternalModuleCache() && path.startsWith(TESTS_DIR) && path.endsWith('.test.js'))
+			? `${code}\nrequire(${JSON.stringify(__filename)}).applyAfterAllHook()\n`
+			: code
+	),
+	{ignoreNodeModules: false, exts: EXTS}
+);

test/support/runner.mjs

@@ -0,0 +1,49 @@
+/* --------------------
+ * livepack
+ * Custom test runner to capture V8 coverage
+ * ------------------*/
+
+// Modules
+import {join as pathJoin} from 'path';
+import {fileURLToPath} from 'url';
+import LightRunner from 'jest-light-runner'; // eslint-disable-line import/no-unresolved
+import assert from 'simple-invariant';
+
+// Constants
+const COVERAGE_PATH = pathJoin(fileURLToPath(import.meta.url), '../coverage.js');
+
+// Exports
+
+/**
+ * Modification of `jest-light-runner`.
+ * If coverage enabled:
+ *   - Adds `./coverage.js` to setup files before `./register.js`
+ *   - Captures V8 coverage data which `./coverage.js` smuggled out via `global.__coverage__`
+ *     and passes it back to Jest.
+ */
+export default class CustomRunner extends LightRunner {
+	runTests(tests, watcher, onStart, onResult, onFailure) {
+		if (this._config.collectCoverage) {
+			const onResultOriginal = onResult;
+			onResult = (test, result) => {
+				result.v8Coverage = result.coverage;
+				result.coverage = undefined;
+				return onResultOriginal(test, result);
+			};
+
+			if (tests.length > 0) {
+				const {context} = tests[0];
+				const setupFilesAfterEnv = [...context.config.setupFilesAfterEnv];
+				setupFilesAfterEnv.splice(setupFilesAfterEnv.length - 1, 0, COVERAGE_PATH);
+				context.config = {...context.config, setupFilesAfterEnv};
+
+				assert(
+					tests.length === 1 || tests[1].context === tests[0].context,
+					'Differing context objects between tests'
+				);
+			}
+		}
+
+		return super.runTests(tests, watcher, onStart, onResult, onFailure);
+	}
+}