toMatch behaves oddly for regex with global flag #9283
Description
🐛 Bug Report
We're upgrading from Jest 23 to 24 and encountered an odd breaking test. When testing a RegExp with the g flag, the regular expression is not reset between assertions, such that subsequent assertions that should pass, fail.
This test passes on Jest 23. It appears this behavior was introduced in c3a0167. Previously, Jest used new RegExp(expected).test(received), but switched to expected.test(received). This causes confusing behavior due to the way that regular expressions with the g or y flag keep a lastIndex.
To Reproduce
Steps to reproduce the behavior:
We have a regex /[f]\d+/ig which matches all instances in a string. In our tests, we test it against several strings:
it('matches on acceptable string formats', () => {
const regex = /[f]\d+/ig;
expect('f567').toMatch(regex);
expect('F12 + 2 / f45').toMatch(regex);
expect('Ff567').toMatch(regex);
expect('f1 2').toMatch(regex);
expect('F12abc + 123 + gf123').toMatch(regex);
});This reports:
Expected pattern: /[f]\d+/gi
Received string: "Ff567"
72 | expect('f567').toMatch(regex);
73 | expect('F12 + 2 / f45').toMatch(regex);
> 74 | expect('Ff567').toMatch(regex);
| ^
75 | expect('f1 2').toMatch(regex);
76 | expect('F12abc + 123 + gf123').toMatch(regex);
77 | });
Expected behavior
All of the above tests should pass.
Link to repl or repo (highly encouraged)
https://repl.it/repls/KaleidoscopicBuzzingEnvironment
envinfo
System:
OS: Linux 4.15 Linux Mint 18.3 (Sylvia)
CPU: (8) x64 Intel(R) Xeon(R) CPU E3-1505M v5 @ 2.80GHz
Binaries:
Node: 10.15.0 - ~/.nvm/versions/node/v10.15.0/bin/node
Yarn: 1.19.2 - /usr/bin/yarn
npm: 6.4.1 - ~/.nvm/versions/node/v10.15.0/bin/npm
npmPackages:
jest: ^24.9.0 => 24.9.0