fix: disallow hook definitions in tests

CHANGELOG.md

@@ -10,6 +10,7 @@
 - `[jest-circus, jest-console, jest-jasmine2, jest-reporters, jest-util, pretty-format]` Fix time durating formatting and consolidate time formatting code ([#9765](https://github.com/facebook/jest/pull/9765))
 - `[jest-circus]` [**BREAKING**] Fail tests if a test takes a done callback and have return values ([#9129](https://github.com/facebook/jest/pull/9129))
 - `[jest-circus]` [**BREAKING**] Throw a proper error if a test / hook is defined asynchronously ([#8096](https://github.com/facebook/jest/pull/8096))
+- `[jest-circus]` Throw more descriptive error if hook is defined inside test ([#9957](https://github.com/facebook/jest/pull/9957))
 - `[jest-config, jest-resolve]` [**BREAKING**] Remove support for `browser` field ([#9943](https://github.com/facebook/jest/pull/9943))
 
 ### Chore & Maintenance

e2e/__tests__/nestedTestDefinitions.test.ts

@@ -55,3 +55,17 @@ test('print correct message when nesting describe inside it', () => {
     'Cannot nest a describe inside a test. Describe block "inner describe" cannot run because it is nested within "test".',
   );
 });
+
+test('print correct message when nesting a hook inside it', () => {
+  if (!isJestCircusRun()) {
+    return;
+  }
+
+  const result = runJest('nested-test-definitions', ['nestedHookInTest']);
+
+  expect(result.exitCode).toBe(1);
+
+  expect(result.stderr).toContain(
+    'Hooks cannot be defined inside tests. Hook of type "beforeEach" is nested within "test".',
+  );
+});

e2e/nested-test-definitions/__tests__/nestedHookInTest.js

@@ -0,0 +1,18 @@
+/**
+ * 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';
+
+const {getTruthy} = require('../index');
+
+test('test', () => {
+  expect(getTruthy()).toBeTruthy();
+
+  beforeEach(() => {
+    // nothing to see here
+  });
+});

packages/jest-circus/src/eventHandler.ts

@@ -88,8 +88,15 @@ const eventHandler: Circus.EventHandler = (
       break;
     }
     case 'add_hook': {
-      const {currentDescribeBlock, hasStarted} = state;
+      const {currentDescribeBlock, currentlyRunningTest, hasStarted} = state;
       const {asyncError, fn, hookType: type, timeout} = event;
+
+      if (currentlyRunningTest) {
+        throw new Error(
+          `Hooks cannot be defined inside tests. Hook of type "${type}" is nested within "${currentlyRunningTest.name}".`,
+        );
+      }
+
       const parent = currentDescribeBlock;
 
       if (hasStarted) {