Enable conditional exports, ES module named exports

.gitignore

@@ -4,6 +4,7 @@
 !lib/
 !settings.js
 !versions.js
+!istanbul-loader-hook.mjs
 !package.json
 !package-lock.json
 !README.md

coverage-map.js

@@ -5,6 +5,9 @@ const rootFiles = ['settings', 'versions'];
 
 module.exports = t => {
   const parts = path.relative(process.cwd(), path.resolve(t)).split(/\\|\//)
+  if (parts[1] === 'libtap.mjs')
+    return 'lib/tap.mjs'
+
   const unit = path.basename(parts[1], '.js')
   if (rootFiles.includes(unit))
     return `${unit}.js`

istanbul-loader-hook.mjs

@@ -0,0 +1,14 @@
+import { fileURLToPath } from 'url'
+import babel from '@babel/core'
+
+export async function transformSource(source, context, defaultTransformSource) {
+	const {code} = await babel.transformAsync(source, {
+		babelrc: false,
+		configFile: false,
+		filename: fileURLToPath(context.url),
+		sourceMaps: 'inline',
+		plugins: ['babel-plugin-istanbul']
+	})
+
+	return {source: code}
+}

lib/tap.mjs

@@ -0,0 +1,31 @@
+import tap from './tap.js'
+
+export const {
+  Test, Spawn, Stdin,
+  spawn, sub,
+  todo, skip, only, test,
+  stdinOnly, stdin,
+  bailout,
+  comment,
+  timeout,
+  main,
+  process,
+  processSubtest,
+  addAssert,
+  pragma,
+  plan, end,
+  beforeEach,
+  afterEach,
+  teardown,
+  autoend,
+  pass, fail, ok, notOk,
+  emits,
+  error, equal, not, same, notSame, strictSame, strictNotSame,
+  testdir, fixture,
+  matchSnapshot,
+  hasStrict, match, notMatch, type,
+  expectUncaughtException, throwsArgs, throws, doesNotThrow,
+  rejects, resolves, resolveMatch, resolveMatchSnapshot
+} = tap
+
+export default tap

npm-run-test.js

@@ -4,14 +4,21 @@
 const foregroundChild = require('foreground-child')
 
 async function runTests() {
+  const semver = require('semver')
   const glob = require('glob')
   const os = require('os')
   const t = require('.')
   const coverageMap = require('./coverage-map.js')
+  const testESM = semver.gte(process.versions.node, '13.10.0')
+  const testFileGlob = testESM ? 'test/**/*.{js,mjs}' : 'test/**/*.js'
+  const esLoaderHook = {
+    NODE_OPTIONS: `${process.env.NODE_OPTIONS || ''} --experimental-loader "${require.resolve('./istanbul-loader-hook.mjs')}"`
+  }
 
   t.jobs = os.cpus().length
 
-  glob.sync('test/**/*.js').forEach(file => {
+  glob.sync(testFileGlob).forEach(file => {
+    const esLoaderEnv = file.endsWith('.mjs') ? esLoaderHook : {}
     t.spawn(
       process.execPath,
       [file],
@@ -20,7 +27,8 @@ async function runTests() {
           ...process.env,
           NYC_CONFIG_OVERRIDE: JSON.stringify({
             include: coverageMap(file) || ''
-          })
+          }),
+          ...esLoaderEnv
         }
       },
       file

nyc.config.js

@@ -1,12 +1,15 @@
 'use strict'
 
+const semver = require('semver')
+
 module.exports = {
   all: true,
   checkCoverage: true,
   lines: 100,
   functions: 100,
   branches: 100,
   statements: 100,
+  extension: semver.gte(process.versions.node, '13.10.0') ? ['.js', '.mjs'] : ['.js'],
   include: [
     'settings.js',
     'versions.js',