Add tests for --require ESM

As both .mjs and type=module (combined with cjs for good measure).

Updated linter to allow tests to use spread operator (ecmaVersion 2018)

Allow --require'd module to be an object, or "module"

.eslintrc.yml

@@ -56,6 +56,8 @@ overrides:
       browser: false
   - files:
       - test/**/*.{js,mjs}
+    parserOptions:
+      ecmaVersion: 2018
     env:
       mocha: true
     globals:

lib/cli/run-helpers.js

@@ -92,7 +92,10 @@ exports.handleRequires = async (requires = []) => {
       debug('resolved required file %s to %s', mod, modpath);
     }
     const requiredModule = await requireOrImport(modpath);
-    if (type(requiredModule) === 'object' && requiredModule.mochaHooks) {
+    if (
+      ['object', 'module'].includes(type(requiredModule)) &&
+      requiredModule.mochaHooks
+    ) {
       const mochaHooksType = type(requiredModule.mochaHooks);
       if (/function$/.test(mochaHooksType) || mochaHooksType === 'object') {
         debug('found root hooks in required file %s', mod);

test/integration/fixtures/options/require/esm/package.json

@@ -0,0 +1 @@
+{ "type": "module" }

test/integration/fixtures/options/require/esm/root-hook-defs-esm.fixture.js

@@ -0,0 +1,8 @@
+export const mochaHooks = () => ({
+  beforeEach() {
+    console.log('esm beforeEach');
+  },
+  afterEach() {
+    console.log('esm afterEach');
+  },
+});

test/integration/fixtures/options/require/root-hook-defs-esm.fixture.mjs

@@ -0,0 +1,8 @@
+export const mochaHooks = {
+  beforeAll() {
+    console.log('mjs beforeAll');
+  },
+  afterAll() {
+    console.log('mjs afterAll');
+  },
+};

test/integration/options/require.spec.js

@@ -1,6 +1,7 @@
 'use strict';
 
 var invokeMochaAsync = require('../helpers').invokeMochaAsync;
+var utils = require('../../../lib/utils');
 
 describe('--require', function() {
   describe('when mocha run in serial mode', function() {
@@ -45,6 +46,51 @@ describe('--require', function() {
         /beforeAll[\s\S]+?beforeAll array 1[\s\S]+?beforeAll array 2[\s\S]+?beforeEach[\s\S]+?beforeEach array 1[\s\S]+?beforeEach array 2[\s\S]+?afterEach[\s\S]+?afterEach array 1[\s\S]+?afterEach array 2[\s\S]+?afterAll[\s\S]+?afterAll array 1[\s\S]+?afterAll array 2/
       );
     });
+
+    describe.only('support ESM when style=module or .mjs extension', function() {
+      before(function() {
+        if (!utils.supportsEsModules()) this.skip();
+      });
+
+      it('should run root hooks when provided via mochaHooks', function() {
+        return expect(
+          invokeMochaAsync(
+            [
+              '--require=' +
+                require.resolve(
+                  // as object
+                  '../fixtures/options/require/root-hook-defs-esm.fixture.mjs'
+                ),
+              '--require=' +
+                require.resolve(
+                  // as function
+                  '../fixtures/options/require/esm/root-hook-defs-esm.fixture.js'
+                ),
+              '--require=' +
+                require.resolve(
+                  // mixed with commonjs
+                  '../fixtures/options/require/root-hook-defs-a.fixture.js'
+                ),
+              require.resolve(
+                '../fixtures/options/require/root-hook-test.fixture.js'
+              )
+            ],
+            {
+              env: {
+                ...process.env,
+                NODE_OPTIONS:
+                  +process.versions.node.split('.')[0] >= 13
+                    ? ''
+                    : '--experimental-modules'
+              }
+            }
+          )[1],
+          'when fulfilled',
+          'to contain output',
+          /mjs beforeAll[\s\S]+?beforeAll[\s\S]+?esm beforeEach[\s\S]+?beforeEach[\s\S]+?esm afterEach[\s\S]+?afterEach[\s\S]+?mjs afterAll[\s\S]+?afterAll/
+        );
+      });
+    });
   });
 
   describe('when mocha in parallel mode', function() {