fix: throw on nested test declarations

CHANGELOG.md

@@ -10,6 +10,7 @@
 ### Fixes
 
 - `[expect]` Restore support for passing functions to `toHaveLength` matcher ([#9796](https://github.com/facebook/jest/pull/9796))
+- `[jest-circus]` Throw on nested test definitions ([#9828](https://github.com/facebook/jest/pull/9828))
 - `[jest-changed-files]` `--only-changed` should include staged files ([#9799](https://github.com/facebook/jest/pull/9799))
 - `[jest-each]` `each` will throw an error when called with too many arguments ([#9818](https://github.com/facebook/jest/pull/9818))
 

e2e/__tests__/__snapshots__/nestedTestDefinitions.test.ts.snap

@@ -0,0 +1,40 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`print correct error message with nested test definitions inside describe 1`] = `
+FAIL __tests__/nestedTestWithinDescribe.js
+  in describe
+    ✕ outer test
+
+  ● in describe › outer test
+
+    Tests cannot be nested. Test "inner test" cannot run because it is nested within "outer test".
+
+      14 |     expect(getTruthy()).toBeTruthy();
+      15 | 
+    > 16 |     test('inner test', () => {
+         |     ^
+      17 |       expect(getTruthy()).toBeTruthy();
+      18 |     });
+      19 |   });
+
+      at Object.test (__tests__/nestedTestWithinDescribe.js:16:5)
+`;
+
+exports[`print correct error message with nested test definitions outside describe 1`] = `
+FAIL __tests__/nestedTestOutsideDescribe.js
+  ✕ outer test
+
+  ● outer test
+
+    Tests cannot be nested. Test "inner test" cannot run because it is nested within "outer test".
+
+      13 |   expect(getTruthy()).toBeTruthy();
+      14 | 
+    > 15 |   test('inner test', () => {
+         |   ^
+      16 |     expect(getTruthy()).toEqual('This test should not have run');
+      17 |   });
+      18 | });
+
+      at Object.test (__tests__/nestedTestOutsideDescribe.js:15:3)
+`;

e2e/__tests__/nestedTestDefinitions.test.ts

@@ -0,0 +1,57 @@
+/**
+ * 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 {wrap} from 'jest-snapshot-serializer-raw';
+import {isJestCircusRun} from '@jest/test-utils';
+import runJest from '../runJest';
+import {extractSummary} from '../Utils';
+
+const cleanupRunnerStack = (stderr: string) =>
+  wrap(
+    stderr
+      .split('\n')
+      .filter(
+        line =>
+          !line.includes('packages/jest-jasmine2/build') &&
+          !line.includes('packages/jest-circus/build'),
+      )
+      .join('\n'),
+  );
+
+test('print correct error message with nested test definitions outside describe', () => {
+  const result = runJest('nested-test-definitions', ['outside']);
+
+  expect(result.exitCode).toBe(1);
+
+  const summary = extractSummary(result.stderr);
+
+  expect(cleanupRunnerStack(summary.rest)).toMatchSnapshot();
+});
+
+test('print correct error message with nested test definitions inside describe', () => {
+  const result = runJest('nested-test-definitions', ['within']);
+
+  expect(result.exitCode).toBe(1);
+
+  const summary = extractSummary(result.stderr);
+
+  expect(cleanupRunnerStack(summary.rest)).toMatchSnapshot();
+});
+
+test('print correct message when nesting describe inside it', () => {
+  if (!isJestCircusRun()) {
+    return;
+  }
+
+  const result = runJest('nested-test-definitions', ['nestedDescribeInTest']);
+
+  expect(result.exitCode).toBe(1);
+
+  expect(result.stderr).toContain(
+    'Cannot nest a describe inside a test. Describe block "inner describe" cannot run because it is nested within "test".',
+  );
+});

e2e/nested-test-definitions/__tests__/nestedDescribeInTest.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();
+
+  describe('inner describe', () => {
+    // nothing to see here
+  });
+});

e2e/nested-test-definitions/__tests__/nestedTestOutsideDescribe.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('outer test', () => {
+  expect(getTruthy()).toBeTruthy();
+
+  test('inner test', () => {
+    expect(getTruthy()).toEqual('This test should not have run');
+  });
+});

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

@@ -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.
+ */
+
+'use strict';
+
+const {getTruthy} = require('../index');
+
+describe('in describe', () => {
+  test('outer test', () => {
+    expect(getTruthy()).toBeTruthy();
+
+    test('inner test', () => {
+      expect(getTruthy()).toBeTruthy();
+    });
+  });
+});

e2e/nested-test-definitions/index.js

@@ -0,0 +1,10 @@
+/**
+ * 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';
+
+module.exports.getTruthy = () => true;

e2e/nested-test-definitions/package.json

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

packages/jest-circus/src/eventHandler.ts

@@ -36,7 +36,14 @@ const eventHandler: Circus.EventHandler = (
     }
     case 'start_describe_definition': {
       const {blockName, mode} = event;
-      const {currentDescribeBlock} = state;
+      const {currentDescribeBlock, currentlyRunningTest} = state;
+
+      if (currentlyRunningTest) {
+        throw new Error(
+          `Cannot nest a describe inside a test. Describe block "${blockName}" cannot run because it is nested within "${currentlyRunningTest.name}".`,
+        );
+      }
+
       const describeBlock = makeDescribe(blockName, currentDescribeBlock, mode);
       currentDescribeBlock.children.push(describeBlock);
       state.currentDescribeBlock = describeBlock;
@@ -88,8 +95,15 @@ const eventHandler: Circus.EventHandler = (
       break;
     }
     case 'add_test': {
-      const {currentDescribeBlock} = state;
+      const {currentDescribeBlock, currentlyRunningTest} = state;
       const {asyncError, fn, mode, testName: name, timeout} = event;
+
+      if (currentlyRunningTest) {
+        throw new Error(
+          `Tests cannot be nested. Test "${name}" cannot run because it is nested within "${currentlyRunningTest.name}".`,
+        );
+      }
+
       const test = makeTest(
         fn,
         mode,

packages/jest-jasmine2/src/jasmine/Env.ts

@@ -566,11 +566,7 @@ export default function (j$: Jasmine) {
         // This check throws an error to warn the user about the edge-case.
         if (currentSpec !== null) {
           throw new Error(
-            'Tests cannot be nested. Test `' +
-              spec.description +
-              '` cannot run because it is nested within `' +
-              currentSpec.description +
-              '`.',
+            `Tests cannot be nested. Test "${spec.description}" cannot run because it is nested within "${currentSpec.description}".`,
           );
         }
         currentDeclarationSuite.addChild(spec);