Docs - Expect API - toThrow - Added a note about the type of value thrown

[SSTPIERRE2]

Summary

I and some others have ran into issues where one is testing some code they expect to throw, but the code doesn't specifically throw an instance of Error, the test will simply fail without explanation. This can be due to throwing anything other than new Error(...), where Jest will not recognize what the function has thrown. This addition to the docs merely clarifies that toThrow is specifically looking for an instance of Error.

Test plan

None, simple addition to the docs for clarification.

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[SSTPIERRE2]

Looks like the jest-circus test failed, it doesn't appear related to the readme, but I could be wrong. Please advise, thanks!

[lh0x00]

test-jest-circus is work incorrect sometimes 💃

[pedrottimark]

@SSTPIERRE2 Thank you for contributing to Jest. To help interact on your contribution:

1. Can you say which version?
2. Can you give a few examples of confusing tests that motivate the sentence? The wording might need to become more specific for which type of expected argument in the assertion.

For example, toThrow assertion without argument works for values that are not instance of Error:

test('toThrow without expected value', () => {
  const received = () => {
    throw 13;
  };

  expect(received).toThrow();
  expect(received).not.toThrow();
});

expect(received).not.toThrow()

Thrown value: 13

This improvement in the report from #7621 in Jest 24.0.0 or later

P.S. Yes, ignore test-jest-circus failure on CI

When you edit Jest .md files, you can run locally yarn lint:md before you commit the change

[SimenB]

Rebasing on master should fix CI, fwiw

[codecov-io]

Codecov Report

Merging #8772 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #8772   +/-   ##
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  Coverage   64.13%   64.13%           
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  Files         292      292           
  Lines       12452    12452           
  Branches     3072     3072           
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  Hits         7986     7986           
  Misses       3821     3821           
  Partials      645      645           

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[SimenB]

From #8772 (comment), I don't think the docs change is correct, so closing.

Feel free to open a new PR if I'm mistaken!

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