feature: allow ESM for test environment (#11033)

CHANGELOG.md

@@ -26,6 +26,7 @@
 - `[jest-runner]` [**BREAKING**] set exit code to 1 if test logs after teardown ([#10728](https://github.com/facebook/jest/pull/10728))
 - `[jest-runner]` [**BREAKING**] Run transforms over `runnner` ([#8823](https://github.com/facebook/jest/pull/8823))
 - `[jest-runner]` [**BREAKING**] Run transforms over `testRunnner` ([#8823](https://github.com/facebook/jest/pull/8823))
+- `[jest-runner]` Possibility to use ESM for test environment ([11033](https://github.com/facebook/jest/pull/11033))
 - `[jest-runtime]` Detect reexports from CJS as named exports in ESM ([#10988](https://github.com/facebook/jest/pull/10988))
 - `[jest-runtime]` Support for async code transformations ([#11191](https://github.com/facebook/jest/pull/11191) & [#11220](https://github.com/facebook/jest/pull/11220))
 - `[jest-reporters]` Add static filepath property to all reporters ([#11015](https://github.com/facebook/jest/pull/11015))

e2e/__tests__/testEnvironmentEsm.ts

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {resolve} from 'path';
+import {onNodeVersions} from '@jest/test-utils';
+import runJest from '../runJest';
+
+// The versions where vm.Module exists and commonjs with "exports" is not broken
+onNodeVersions('^12.16.0 || >=13.7.0', () => {
+  it('support test environment written in ESM', () => {
+    const DIR = resolve(__dirname, '../test-environment-esm');
+    const {exitCode} = runJest(DIR);
+
+    expect(exitCode).toBe(0);
+  });
+});

e2e/test-environment-esm/EnvESM.js

@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import NodeEnvironment from 'jest-environment-node';
+
+export default class Env extends NodeEnvironment {
+  constructor(...args) {
+    super(...args);
+    this.global.someVar = 42;
+  }
+}

e2e/test-environment-esm/__tests__/testUsingESMTestEnv.test.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+'use strict';
+
+test('dummy', () => {
+  expect(global.someVar).toBe(42);
+});

e2e/test-environment-esm/package.json

@@ -0,0 +1,7 @@
+{
+  "type": "module",
+  "jest": {
+    "testEnvironment": "<rootDir>/EnvESM.js",
+    "transform": {}
+  }
+}

packages/jest-runner/src/runTest.ts

@@ -6,6 +6,7 @@
  *
  */
 
+import {pathToFileURL} from 'url';
 import chalk = require('chalk');
 import * as fs from 'graceful-fs';
 import sourcemapSupport = require('source-map-support');
@@ -105,10 +106,39 @@ async function runTestInternal(
 
   const cacheFS = new Map([[path, testSource]]);
   const transformer = await createScriptTransformer(config, cacheFS);
-
-  const TestEnvironment: typeof JestEnvironment = interopRequireDefault(
-    transformer.requireAndTranspileModule(testEnvironment),
-  ).default;
+  let TestEnvironment: typeof JestEnvironment;
+  try {
+    TestEnvironment = interopRequireDefault(
+      transformer.requireAndTranspileModule(testEnvironment),
+    ).default;
+  } catch (err) {
+    if (err.code === 'ERR_REQUIRE_ESM') {
+      try {
+        const configUrl = pathToFileURL(testEnvironment);
+
+        // node `import()` supports URL, but TypeScript doesn't know that
+        const importedConfig = await import(configUrl.href);
+
+        if (!importedConfig.default) {
+          throw new Error(
+            `Jest: Failed to load mjs config file ${testEnvironment} - did you use a default export?`,
+          );
+        }
+
+        TestEnvironment = importedConfig.default;
+      } catch (innerError) {
+        if (innerError.message === 'Not supported') {
+          throw new Error(
+            `Jest: Your version of Node does not support dynamic import - please enable it or use a .cjs file extension for file ${testEnvironment}`,
+          );
+        }
+
+        throw innerError;
+      }
+    } else {
+      throw err;
+    }
+  }
   const testFramework: TestFramework = interopRequireDefault(
     transformer.requireAndTranspileModule(
       process.env.JEST_JASMINE === '1' ? 'jest-jasmine2' : config.testRunner,