Fix jest crashing when potentialError is null

CHANGELOG.md

@@ -17,6 +17,7 @@
 - `[jest-mock]` Fix inheritance of static properties and methods in mocks ([#7003](https://github.com/facebook/jest/pull/7003))
 - `[jest-mock]` Fix mocking objects without `Object.prototype` in their prototype chain ([#7003](https://github.com/facebook/jest/pull/7003))
 - `[jest-cli]` Update jest-cli to show git ref in message when using `changedSince` ([#7028](https://github.com/facebook/jest/pull/7028))
+- `[jest-jasmine2`] Fix crash when test return Promise rejected with null ([#7049](https://github.com/facebook/jest/pull/7049))
 
 ### Chore & Maintenance
 

e2e/__tests__/promise_reject.test.js

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ *
+ * @flow
+ */
+'use strict';
+import runJest from '../runJest';
+import path from 'path';
+
+const {cleanup, writeFiles} = require('../Utils');
+const DIR = path.resolve('../promise-reject');
+
+beforeEach(() => cleanup(DIR));
+afterEach(() => cleanup(DIR));
+
+test('', () => {
+  writeFiles(DIR, {
+    'package.json': '{}',
+    'promise_reject.test.js': `
+     test('test', () => {
+       return Promise.reject(null)
+     });
+   `,
+  });
+  const {stdout, stderr, status} = runJest(DIR);
+  expect(stdout).toBe('');
+  expect(stderr).toMatch(/(Failed|thrown): null/);
+  expect(status).toBe(1);
+});

e2e/promise-reject/package.json

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

packages/jest-jasmine2/src/is_error.js

@@ -12,9 +12,11 @@ import prettyFormat from 'pretty-format';
 export default function isError(potentialError: any) {
   // duck-type Error, see #2549
   const isError =
+    potentialError !== null &&
     typeof potentialError === 'object' &&
     typeof potentialError.message === 'string' &&
     typeof potentialError.name === 'string';
+
   const message = isError
     ? null
     : `Failed: ${prettyFormat(potentialError, {maxDepth: 3})}`;