Invalid toThrow verification

🐛 Bug Report

.toThrow() fails to check correctly against an empty string or a string with one symbol.

To Reproduce

it('must fail when compared against an empty string', () => {
    expect(() => {
        throw 'something';
     }).toThrow(''); // PASS
});

it('must fail against a string with one letter', () => {
    expect(() => {
        throw 'something';
     }).toThrow('a'); // PASS
});

Expected behavior

The two cases above are supposed to fail. But instead, they both succeed.

Curiously, if in the second case we use more than one letter, only then the test fails.

[thymikee]

Nah, I like the current behavior and wouldn’t change it. It’s been like this forever and users didn’t mind.

[SimenB]

The first one passes since we convert it to a regex (empty regexp is the same as /(?:)/, so it matches anything)

https://github.com/facebook/jest/blob/c9893d2f1cdbc98655ca446d2a49f8c77a42b4be/packages/expect/src/to_throw_matchers.js#L53-L55

'something'.match(new RegExp('')) // returns [''], which is considered a match

@thymikee @rickhanlonii should we drop the regexp conversion for empty strings? My guess the current behaviour exists to allow substring matches, but using .includes won’t help for empty strings.