[expect]: add empty string check to toThrow matcher

CHANGELOG.md

@@ -29,6 +29,7 @@
 - `[jest-jasmine2]` Fail synchronous test timeouts ([#7074](https://github.com/facebook/jest/pull/7074))
 - `[jest-jasmine2]` Better error message when a describe block is empty ([#6372](https://github.com/facebook/jest/pull/6372))
 - `[jest-circus]` Better error message when a describe block is empty ([#6372](https://github.com/facebook/jest/pull/6372))
+- `[expect]` Add empty string check to `toThrow` matcher ([#6836](https://github.com/facebook/jest/pull/6836))
 
 ### Chore & Maintenance
 

packages/expect/src/__tests__/__snapshots__/to_throw_matchers.test.js.snap

@@ -28,6 +28,16 @@ Instead, it threw:
 <red>      <dim>at jestExpect (</>packages/expect/src/__tests__/toThrowMatchers-test.js<dim>:24:74)</></>"
 `;
 
+exports[`.toThrow() fails when given an empty string 1`] = `
+"<dim>expect(</><red>function</><dim>).toThrow(</><green>string</><dim>)</>
+
+Expected the function to throw an error matching:
+  <green>\\"\\"</>
+Instead, it threw:
+<red>  Error</>
+<red>      <dim>at jestExpect (</>packages/expect/src/__tests__/toThrowMatchers-test.js<dim>:24:74)</></>"
+`;
+
 exports[`.toThrow() invalid actual 1`] = `
 "<dim>expect(</><red>function</><dim>).toThrow(</><green>undefined</><dim>)</>
 
@@ -153,6 +163,16 @@ Instead, it threw:
 <red>      <dim>at jestExpect (</>packages/expect/src/__tests__/toThrowMatchers-test.js<dim>:24:74)</></>"
 `;
 
+exports[`.toThrowError() fails when given an empty string 1`] = `
+"<dim>expect(</><red>function</><dim>).toThrow(</><green>string</><dim>)</>
+
+Expected the function to throw an error matching:
+  <green>\\"\\"</>
+Instead, it threw:
+<red>  Error</>
+<red>      <dim>at jestExpect (</>packages/expect/src/__tests__/toThrowMatchers-test.js<dim>:24:74)</></>"
+`;
+
 exports[`.toThrowError() invalid actual 1`] = `
 "<dim>expect(</><red>function</><dim>).toThrowError(</><green>undefined</><dim>)</>
 

packages/expect/src/__tests__/to_throw_matchers.test.js

@@ -28,6 +28,14 @@ class customError extends Error {
     class Err extends customError {}
     class Err2 extends customError {}
 
+    test('fails when given an empty string', () => {
+      expect(() =>
+        jestExpect(() => {
+          throw new customError('apple');
+        }).toThrow(''),
+      ).toThrowErrorMatchingSnapshot();
+    });
+
     test('to throw or not to throw', () => {
       jestExpect(() => {
         throw new customError('apple');

packages/expect/src/to_throw_matchers.js

@@ -51,7 +51,11 @@ export const createMatcher = (matcherName: string, fromPromise?: boolean) => (
   }
 
   if (typeof expected === 'string') {
-    expected = new RegExp(escapeStrForRegex(expected));
+    if (expected === '') {
+      expected = new RegExp('^$');
+    } else {
+      expected = new RegExp(escapeStrForRegex(expected));
+    }
   }
 
   if (typeof expected === 'function') {

packages/jest-regex-util/src/__tests__/index.test.js

@@ -1,6 +1,6 @@
 jest.mock('path');
 
-import {replacePathSepForRegex} from '../index';
+import {replacePathSepForRegex, escapeStrForRegex} from '../index';
 import path from 'path';
 
 describe('replacePathSepForRegex()', () => {
@@ -13,6 +13,12 @@ describe('replacePathSepForRegex()', () => {
     });
   });
 
+  describe('escapeStrForRegex', () => {
+    it('returns regex for given string: [0-9]', () => {
+      expect(escapeStrForRegex('[0-9]')).toBe('\\[0-9\\]');
+    });
+  });
+
   describe('win32', () => {
     beforeEach(() => (path.sep = '\\'));