feat: add @jest/globals package for importing globals explicitly

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+- `[@jest/globals]` New package so Jest's globals can be explicitly imported ([#9801](https://github.com/facebook/jest/pull/9801))
+
 ### Fixes
 
 - `[expect]` Restore support for passing functions to `toHaveLength` matcher ([#9796](https://github.com/facebook/jest/pull/9796))

docs/GlobalAPI.md

@@ -3,7 +3,7 @@ id: api
 title: Globals
 ---
 
-In your test files, Jest puts each of these methods and objects into the global environment. You don't have to require or import anything to use them.
+In your test files, Jest puts each of these methods and objects into the global environment. You don't have to require or import anything to use them. However, if you prefer explicit imports, you can do `import {describe, expect, it} from '@jest/globals'`.
 
 ## Methods
 

docs/JestObjectAPI.md

@@ -3,7 +3,7 @@ id: jest-object
 title: The Jest Object
 ---
 
-The `jest` object is automatically in scope within every test file. The methods in the `jest` object help create mocks and let you control Jest's overall behavior.
+The `jest` object is automatically in scope within every test file. The methods in the `jest` object help create mocks and let you control Jest's overall behavior. It can also be imported explicitly by via `import {jest} from '@jest/globals'`.
 
 ## Mock Modules
 

e2e/__tests__/importedGlobals.test.ts

@@ -0,0 +1,13 @@
+/**
+ * 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 runJest from '../runJest';
+
+test('imported globals', () => {
+  const result = runJest('imported-globals');
+  expect(result.exitCode).toBe(0);
+});

e2e/imported-globals/__tests__/env.test.js

@@ -0,0 +1,22 @@
+/**
+ * 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 {
+  expect as importedExpect,
+  jest as importedJest,
+  test as importedTest,
+} from '@jest/globals';
+
+importedTest('they match the globals', () => {
+  importedExpect(importedExpect).toBe(expect);
+  importedExpect(importedJest).toBe(jest);
+  importedExpect(importedTest).toBe(test);
+
+  expect(importedExpect).toBe(expect);
+  expect(importedJest).toBe(jest);
+  expect(importedTest).toBe(test);
+});

e2e/imported-globals/babel.config.js

@@ -0,0 +1,8 @@
+/**
+ * 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.
+ */
+
+module.exports = require('../../babel.config');

e2e/imported-globals/package.json

@@ -0,0 +1,5 @@
+{
+  "jest": {
+    "testEnvironment": "node"
+  }
+}

packages/jest-circus/src/legacy-code-todo-rewrite/jestAdapter.ts

@@ -12,7 +12,8 @@ import type {TestResult} from '@jest/test-result';
 import type {RuntimeType as Runtime} from 'jest-runtime';
 import type {SnapshotStateType} from 'jest-snapshot';
 
-const FRAMEWORK_INITIALIZER = require.resolve('./jestAdapterInit');
+const FRAMEWORK_INITIALIZER = path.resolve(__dirname, './jestAdapterInit.js');
+const EXPECT_INITIALIZER = path.resolve(__dirname, './jestExpect.js');
 
 const jestAdapter = async (
   globalConfig: Config.GlobalConfig,
@@ -24,15 +25,13 @@ const jestAdapter = async (
   const {
     initialize,
     runAndTransformResultsToJestFormat,
-  } = runtime.requireInternalModule(FRAMEWORK_INITIALIZER);
+  } = runtime.requireInternalModule<typeof import('./jestAdapterInit')>(
+    FRAMEWORK_INITIALIZER,
+  );
 
   runtime
-    .requireInternalModule<typeof import('./jestExpect')>(
-      path.resolve(__dirname, './jestExpect.js'),
-    )
-    .default({
-      expand: globalConfig.expand,
-    });
+    .requireInternalModule<typeof import('./jestExpect')>(EXPECT_INITIALIZER)
+    .default({expand: globalConfig.expand});
 
   const getPrettier = () =>
     config.prettierPath ? require(config.prettierPath) : null;

packages/jest-globals/.npmignore

@@ -0,0 +1,5 @@
+**/__mocks__/**
+**/__tests__/**
+src
+tsconfig.json
+tsconfig.tsbuildinfo

packages/jest-globals/package.json

@@ -0,0 +1,30 @@
+{
+  "name": "@jest/globals",
+  "version": "25.3.0",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/facebook/jest.git",
+    "directory": "packages/jest-globals"
+  },
+  "engines": {
+    "node": ">= 8.3"
+  },
+  "license": "MIT",
+  "main": "build/index.js",
+  "types": "build/index.d.ts",
+  "typesVersions": {
+    "<3.8": {
+      "build/*": [
+        "build/ts3.4/*"
+      ]
+    }
+  },
+  "dependencies": {
+    "@jest/environment": "^25.3.0",
+    "@jest/types": "^25.3.0",
+    "expect": "^25.3.0"
+  },
+  "publishConfig": {
+    "access": "public"
+  }
+}

packages/jest-globals/src/__tests__/index.ts

@@ -0,0 +1,12 @@
+/**
+ * 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.
+ */
+
+test('throw when directly imported', () => {
+  expect(() => require('../')).toThrowError(
+    'Do not import `@jest/globals` outside of the Jest test environment',
+  );
+});

packages/jest-globals/src/index.ts

@@ -0,0 +1,27 @@
+/**
+ * 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 importedExpect = require('expect');
+import type {Jest} from '@jest/environment';
+import type {Global} from '@jest/types';
+
+export declare type jest = Jest;
+
+export declare type expect = typeof importedExpect;
+
+export declare type it = Global.GlobalAdditions['it'];
+export declare type test = Global.GlobalAdditions['test'];
+export declare type fit = Global.GlobalAdditions['fit'];
+export declare type xit = Global.GlobalAdditions['xit'];
+export declare type xtest = Global.GlobalAdditions['xtest'];
+export declare type describe = Global.GlobalAdditions['describe'];
+export declare type xdescribe = Global.GlobalAdditions['xdescribe'];
+export declare type fdescribe = Global.GlobalAdditions['fdescribe'];
+
+throw new Error(
+  'Do not import `@jest/globals` outside of the Jest test environment',
+);

packages/jest-globals/tsconfig.json

@@ -0,0 +1,14 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    // we don't want `@types/jest` to be referenced
+    "types": ["node"],
+    "rootDir": "src",
+    "outDir": "build"
+  },
+  "references": [
+    {"path": "../expect"},
+    {"path": "../jest-environment"},
+    {"path": "../jest-types"}
+  ]
+}

packages/jest-runtime/package.json

@@ -19,6 +19,7 @@
   "dependencies": {
     "@jest/console": "^25.3.0",
     "@jest/environment": "^25.3.0",
+    "@jest/globals": "^25.3.0",
     "@jest/source-map": "^25.2.6",
     "@jest/test-result": "^25.3.0",
     "@jest/transform": "^25.3.0",

packages/jest-runtime/src/index.ts

@@ -17,6 +17,7 @@ import type {
   Module,
   ModuleWrapper,
 } from '@jest/environment';
+import type * as JestGlobals from '@jest/globals';
 import type {SourceMapRegistry} from '@jest/source-map';
 import {formatStackTrace, separateMessageFromStack} from 'jest-message-util';
 import {createDirectory, deepCyclicCopy} from 'jest-util';
@@ -42,6 +43,19 @@ import Resolver = require('jest-resolve');
 import Snapshot = require('jest-snapshot');
 import stripBOM = require('strip-bom');
 
+type JestGlobalsValues = {
+  jest: JestGlobals.jest;
+  expect: JestGlobals.expect;
+  it: JestGlobals.it;
+  test: JestGlobals.test;
+  fit: JestGlobals.fit;
+  xit: JestGlobals.xit;
+  xtest: JestGlobals.xtest;
+  describe: JestGlobals.describe;
+  xdescribe: JestGlobals.xdescribe;
+  fdescribe: JestGlobals.fdescribe;
+};
+
 type HasteMapOptions = {
   console?: Console;
   maxWorkers: number;
@@ -133,6 +147,7 @@ class Runtime {
   private _unmockList: RegExp | undefined;
   private _virtualMocks: BooleanObject;
   private _moduleImplementation?: typeof nativeModule.Module;
+  private jestObjectCaches: Map<string, Jest>;
 
   constructor(
     config: Config.ProjectConfig,
@@ -169,6 +184,7 @@ class Runtime {
     this._sourceMapRegistry = Object.create(null);
     this._fileTransforms = new Map();
     this._virtualMocks = Object.create(null);
+    this.jestObjectCaches = new Map();
 
     this._mockMetaDataCache = Object.create(null);
     this._shouldMockModuleCache = Object.create(null);
@@ -323,6 +339,11 @@ class Runtime {
       modulePath = manualMock;
     }
 
+    if (moduleName === '@jest/globals') {
+      // @ts-ignore: we don't care that it's not assignable to T
+      return this.getGlobalsForFile(from);
+    }
+
     if (moduleName && this._resolver.isCoreModule(moduleName)) {
       return this._requireCoreModule(moduleName);
     }
@@ -859,6 +880,13 @@ class Runtime {
       return;
     }
 
+    const jestObject = this._createJestObjectFor(
+      filename,
+      localModule.require as LocalModuleRequire,
+    );
+
+    this.jestObjectCaches.set(filename, jestObject);
+
     try {
       compiledFunction.call(
         localModule.exports,
@@ -868,10 +896,7 @@ class Runtime {
         dirname, // __dirname
         filename, // __filename
         this._environment.global, // global object
-        this._createJestObjectFor(
-          filename,
-          localModule.require as LocalModuleRequire,
-        ), // jest object
+        jestObject, // jest object
         ...this._config.extraGlobals.map(globalVariable => {
           if (this._environment.global[globalVariable]) {
             return this._environment.global[globalVariable];
@@ -1337,6 +1362,31 @@ class Runtime {
 
     throw e;
   }
+
+  private getGlobalsForFile(from: Config.Path): JestGlobalsValues {
+    const jest = this.jestObjectCaches.get(from);
+
+    invariant(jest, 'There should always be a Jest object already');
+
+    return {
+      describe: this._environment.global.describe,
+      expect: this._environment.global.expect,
+      fdescribe: this._environment.global.fdescribe,
+      fit: this._environment.global.fit,
+      it: this._environment.global.it,
+      jest,
+      test: this._environment.global.test,
+      xdescribe: this._environment.global.xdescribe,
+      xit: this._environment.global.xit,
+      xtest: this._environment.global.xtest,
+    };
+  }
+}
+
+function invariant(condition: unknown, message?: string): asserts condition {
+  if (!condition) {
+    throw new Error(message);
+  }
 }
 
 export = Runtime;

packages/jest-runtime/tsconfig.json

@@ -9,6 +9,7 @@
     {"path": "../jest-console"},
     {"path": "../jest-environment"},
     {"path": "../jest-environment-node"},
+    {"path": "../jest-globals"},
     {"path": "../jest-haste-map"},
     {"path": "../jest-message-util"},
     {"path": "../jest-mock"},

packages/jest-types/src/Circus.ts

@@ -16,7 +16,9 @@ export type BlockMode = void | 'skip' | 'only' | 'todo';
 export type TestMode = BlockMode;
 export type TestName = Global.TestName;
 export type TestFn = Global.TestFn;
-export type HookFn = (done?: DoneFn) => Promise<any> | null | undefined;
+export type HookFn = (
+  done?: DoneFn,
+) => Promise<unknown> | null | undefined | void;
 export type AsyncFn = TestFn | HookFn;
 export type SharedHookType = 'afterAll' | 'beforeAll';
 export type HookType = SharedHookType | 'afterEach' | 'beforeEach';

scripts/buildTs.js

@@ -23,6 +23,24 @@ const packagesWithTs = packages.filter(p =>
   fs.existsSync(path.resolve(p, 'tsconfig.json'))
 );
 
+packagesWithTs.forEach(pkgDir => {
+  const pkg = require(pkgDir + '/package.json');
+
+  if (!pkg.types) {
+    throw new Error(`Package ${pkg.name} is missing \`types\` field`);
+  }
+
+  if (!pkg.typesVersions) {
+    throw new Error(`Package ${pkg.name} is missing \`typesVersions\` field`);
+  }
+
+  if (pkg.main.replace(/\.js$/, '.d.ts') !== pkg.types) {
+    throw new Error(
+      `\`main\` and \`types\` field of ${pkg.name} does not match`
+    );
+  }
+});
+
 const args = [
   '--silent',
   'tsc',
@@ -51,24 +69,6 @@ const downlevelArgs = ['--silent', 'downlevel-dts', 'build', 'build/ts3.4'];
 
 console.log(chalk.inverse(' Downleveling TypeScript definition files '));
 
-packagesWithTs.forEach(pkgDir => {
-  const pkg = require(pkgDir + '/package.json');
-
-  if (!pkg.types) {
-    throw new Error(`Package ${pkg.name} is missing \`types\` field`);
-  }
-
-  if (!pkg.typesVersions) {
-    throw new Error(`Package ${pkg.name} is missing \`typesVersions\` field`);
-  }
-
-  if (pkg.main.replace(/\.js$/, '.d.ts') !== pkg.types) {
-    throw new Error(
-      `\`main\` and \`types\` field of ${pkg.name} does not match`
-    );
-  }
-});
-
 // we want to limit the number of processes we spawn
 const cpus = Math.max(1, os.cpus().length - 1);