diff --git a/.eslintrc.json b/.eslintrc.json
index 1b588c63a..fdfc36087 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -120,7 +120,7 @@
       }
     },
     {
-      "files": ["test/mozjs.js"],
+      "files": ["test/mozjs.js", "test/mozjs.mjs"],
       "parserOptions": {
         "ecmaVersion": 6
       },
@@ -141,7 +141,7 @@
       }
     },
     {
-      "files": ["test/main/*-es2018.js"],
+      "files": ["test/main/*-es2018.js", "test/main/*-esm.mjs"],
       "env": {
         "es2018": true
       },
@@ -153,7 +153,7 @@
       }
     },
     {
-      "files": ["test/benchmark/**", "test/es2018/**"],
+      "files": ["test/benchmark/**"],
       "env": {
         "es2017": true
       },
diff --git a/.github/workflows/CI.yaml b/.github/workflows/CI.yaml
index fe9079c70..3c4642546 100644
--- a/.github/workflows/CI.yaml
+++ b/.github/workflows/CI.yaml
@@ -106,8 +106,10 @@ jobs:
           sudo apt-fast install -y libmozjs-68-dev
       - run: npm ci
       - run: npm run build
-      - name: Tests
+      - name: Test mozjs.js
         run: js68 test/mozjs.js
+      - name: Test mozjs.mjs
+        run: js68 -m test/mozjs.mjs
 
   # To reproduce SpiderMonkey 102 builds locally:
   #
@@ -142,8 +144,10 @@ jobs:
           sudo apt-get install -y libmozjs-102-dev
       - run: npm ci
       - run: npm run build
-      - name: Tests
+      - name: Test mozjs.js
         run: js102 test/mozjs.js
+      - name: Test mozjs.mjs
+        run: js102 -m test/mozjs.mjs
 
   # To reproduce SpiderMonkey 115 builds locally:
   #
@@ -178,5 +182,7 @@ jobs:
           sudo apt-get install -y libmozjs-115-dev
       - run: npm ci
       - run: npm run build
-      - name: Tests
+      - name: Test mozjs.js
         run: js115 test/mozjs.js
+      - name: Test mozjs.mjs
+        run: js115 -m test/mozjs.mjs
diff --git a/Gruntfile.js b/Gruntfile.js
index 88a333cc8..f256e7de1 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -128,6 +128,7 @@ module.exports = function (grunt) {
         'test/main/HtmlReporter.js',
         'test/main/modules.js',
         'test/main/modules-es2018.js',
+        'test/main/modules-esm.mjs',
         'test/main/legacy.js',
         'test/main/onUncaughtException.js',
         'test/main/promise.js',
diff --git a/build/tasks/test-on-node.js b/build/tasks/test-on-node.js
index d3df6f1e4..a1610d0c1 100644
--- a/build/tasks/test-on-node.js
+++ b/build/tasks/test-on-node.js
@@ -6,7 +6,7 @@ module.exports = function (grunt) {
 
     const totals = { files: 0, failed: 0 };
     for (const file of this.data) {
-      totals.failed += await new Promise(resolve => runQUnit(file, resolve));
+      totals.failed += await runQUnit(file);
       totals.files++;
     }
 
@@ -28,7 +28,7 @@ module.exports = function (grunt) {
     return require(path);
   }
 
-  function runQUnit (file, runEnd) {
+  async function runQUnit (file) {
     // Resolve current QUnit path and remove it from the require cache
     // to avoid stacking the QUnit logs.
     let QUnit = requireFresh('../../qunit/qunit.js');
@@ -37,9 +37,10 @@ module.exports = function (grunt) {
     global.QUnit = QUnit;
 
     QUnit.config.autostart = false;
-    requireFresh('../../' + file);
-    registerEvents(QUnit, file, runEnd);
+    await import('../../' + file);
+    const runEnd = new Promise(resolve => registerEvents(QUnit, file, resolve));
     QUnit.start();
+    await runEnd;
   }
 
   function registerEvents (QUnit, fileName, callback) {
diff --git a/test/cli/cli-main.js b/test/cli/cli-main.js
index 59dadc790..8af31d97a 100644
--- a/test/cli/cli-main.js
+++ b/test/cli/cli-main.js
@@ -54,22 +54,6 @@ ok 3 config
 # exit code: 1`);
   });
 
-  // TODO: Move to /test/cli/fixtures/
-  QUnit.test('run ESM test suite with import statement', async assert => {
-    const command = ['qunit', '../../es2018/esm.mjs'];
-    const execution = await execute(command);
-
-    assert.equal(execution.code, 0);
-    assert.equal(execution.stderr, '');
-    assert.equal(execution.stdout, `TAP version 13
-ok 1 ESM test suite > sum()
-1..1
-# pass 1
-# skip 0
-# todo 0
-# fail 0`);
-  });
-
   // TODO: Move to /test/cli/fixtures/
   QUnit.test('normal trace with native source map', async assert => {
     const command = ['qunit', 'sourcemap/source.js'];
diff --git a/test/cli/structure.js b/test/cli/structure.js
index e032fc3d3..349887b54 100644
--- a/test/cli/structure.js
+++ b/test/cli/structure.js
@@ -7,16 +7,16 @@ const glob = require('tiny-glob/sync');
 // tests, such as checking for fixture files that aren't used or
 // missing from one of the test targets.
 QUnit.module('structure', () => {
-  QUnit.module('test/main/*.js', () => {
+  QUnit.module('test/main/', () => {
     const files = fs.readdirSync(path.join(__dirname, '..', 'main'))
       .map(file => `main/${file}`);
 
     QUnit.test('files', assert => {
       assert.true(files.length > 5, 'found files');
       assert.deepEqual(
-        files.filter(file => file.endsWith('.js')),
+        files.filter(file => file.endsWith('.js') || file.endsWith('.mjs')),
         files,
-        'js files'
+        'JS files only'
       );
     });
 
@@ -43,13 +43,20 @@ QUnit.module('structure', () => {
       });
     });
 
-    QUnit.test('test/mozjs', assert => {
+    QUnit.test('test/mozjs.js', assert => {
       const contents = fs.readFileSync(path.join(__dirname, '..', 'mozjs.js'), 'utf8');
       files.forEach(file => {
         assert.true(contents.includes(file), file);
       });
     });
 
+    QUnit.test('test/mozjs.mjs', assert => {
+      const contents = fs.readFileSync(path.join(__dirname, '..', 'mozjs.mjs'), 'utf8');
+      files.forEach(file => {
+        assert.true(contents.includes(file), file);
+      });
+    });
+
     QUnit.test('test/webWorker-worker.js', assert => {
       const contents = fs.readFileSync(path.join(__dirname, '..', 'webWorker-worker.js'), 'utf8');
       files.forEach(file => {
diff --git a/test/es2018/sum.mjs b/test/dynamic-import/sum.mjs
similarity index 100%
rename from test/es2018/sum.mjs
rename to test/dynamic-import/sum.mjs
diff --git a/test/es2018/esm.mjs b/test/es2018/esm.mjs
deleted file mode 100644
index ca17f7a3c..000000000
--- a/test/es2018/esm.mjs
+++ /dev/null
@@ -1,7 +0,0 @@
-import sum from './sum.mjs';
-
-QUnit.module('ESM test suite', () => {
-  QUnit.test('sum()', assert => {
-    assert.equal(5, sum(2, 3));
-  });
-});
diff --git a/test/index-es5.html b/test/index-es5.html
index 91ad6befa..8d48d117c 100644
--- a/test/index-es5.html
+++ b/test/index-es5.html
@@ -22,6 +22,7 @@
   <script src="main/HtmlReporter.js"></script>
   <script src="main/modules.js"></script>
   <!-- <script src="main/modules-es2018.js"></script> -->
+  <!-- <script src="main/modules-esm.mjs" type="module"></script> -->
   <script src="main/legacy.js"></script>
   <script src="main/onUncaughtException.js"></script>
   <script src="main/promise.js"></script>
diff --git a/test/index.html b/test/index.html
index 356321617..afc7bbc1f 100644
--- a/test/index.html
+++ b/test/index.html
@@ -22,6 +22,7 @@
   <script src="main/HtmlReporter.js"></script>
   <script src="main/modules.js"></script>
   <script src="main/modules-es2018.js"></script>
+  <script src="main/modules-esm.mjs" type="module"></script>
   <script src="main/legacy.js"></script>
   <script src="main/onUncaughtException.js"></script>
   <script src="main/promise.js"></script>
diff --git a/test/main/modules-esm.mjs b/test/main/modules-esm.mjs
new file mode 100644
index 000000000..f747b0125
--- /dev/null
+++ b/test/main/modules-esm.mjs
@@ -0,0 +1,7 @@
+import sum from '../dynamic-import/sum.mjs';
+
+QUnit.module('modules [esm]', () => {
+  QUnit.test('example', assert => {
+    assert.equal(5, sum(2, 3));
+  });
+});
diff --git a/test/main/setTimeout.js b/test/main/setTimeout.js
index 4b00f71dc..e3f9f4e87 100644
--- a/test/main/setTimeout.js
+++ b/test/main/setTimeout.js
@@ -1,12 +1,14 @@
-(function (globalThis) {
+(function () {
+  // eslint-disable-next-line no-undef
+  var global = typeof globalThis !== 'undefined' ? globalThis : window;
   QUnit.module('Support for mocked setTimeout', {
     beforeEach: function () {
-      this.setTimeout = globalThis.setTimeout;
-      globalThis.setTimeout = function () {};
+      this.setTimeout = global.setTimeout;
+      global.setTimeout = function () {};
     },
 
     afterEach: function () {
-      globalThis.setTimeout = this.setTimeout;
+      global.setTimeout = this.setTimeout;
     }
   });
 
@@ -17,6 +19,4 @@
   QUnit.test('test two', function (assert) {
     assert.true(true);
   });
-}((function () {
-  return this;
-}())));
+}());
diff --git a/test/mozjs.js b/test/mozjs.js
index 0697ed53e..b0ac0ff96 100644
--- a/test/mozjs.js
+++ b/test/mozjs.js
@@ -24,6 +24,7 @@ loadRelativeToScript('../test/main/each.js');
 loadRelativeToScript('../test/main/HtmlReporter.js');
 // loadRelativeToScript( "../test/main/modules.js" ); // Requires setTimeout
 loadRelativeToScript('../test/main/modules-es2018.js');
+// import('../test/main/modules-esm.mjs').then(…); // Covered by mozjs.mjs
 loadRelativeToScript('../test/main/legacy.js');
 loadRelativeToScript('../test/main/onUncaughtException.js');
 loadRelativeToScript('../test/main/promise.js');
diff --git a/test/mozjs.mjs b/test/mozjs.mjs
new file mode 100644
index 000000000..de9517911
--- /dev/null
+++ b/test/mozjs.mjs
@@ -0,0 +1,34 @@
+import '../qunit/qunit.js';
+
+// Sync with test/index.html
+import '../test/main/assert.js';
+import '../test/main/assert-es6.js';
+import '../test/main/assert-step.js';
+// import  "../test/main/assert-timeout.js"; // Requires setTimeout
+// import  "../test/main/async.js"; // Requires setTimeout
+import '../test/main/deepEqual.js';
+import '../test/main/diff.js';
+import '../test/main/dump.js';
+import '../test/main/each.js';
+import '../test/main/HtmlReporter.js';
+// import  "../test/main/modules.js"; // Requires setTimeout
+import '../test/main/modules-es2018.js';
+import '../test/main/modules-esm.mjs';
+import '../test/main/legacy.js';
+import '../test/main/onUncaughtException.js';
+import '../test/main/promise.js';
+import '../test/main/setTimeout.js';
+import '../test/main/stacktrace.js';
+import '../test/main/test.js';
+import '../test/main/utilities.js';
+
+QUnit.reporters.tap.init(QUnit);
+QUnit.on('runEnd', (suiteEnd) => {
+  if (suiteEnd.status === 'failed') {
+    // There is no built-in function for sending a non-zero exit code,
+    // so throw an uncaught error to make this happen.
+    throw new Error('Test run has failures.');
+  }
+});
+
+QUnit.start();
diff --git a/test/webWorker-worker.js b/test/webWorker-worker.js
index b9464a05e..f6b92abee 100644
--- a/test/webWorker-worker.js
+++ b/test/webWorker-worker.js
@@ -18,6 +18,7 @@ importScripts(
   'main/HtmlReporter.js',
   'main/modules.js',
   'main/modules-es2018.js',
+  // TODO: 'main/modules-esm.mjs',
   'main/legacy.js',
   'main/onUncaughtException.js',
   'main/promise.js',