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doc: note assert.throws() pitfall #6029

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doc: note assert.throws() pitfall #6029

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21 changes: 19 additions & 2 deletions doc/api/assert.markdown
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Expand Up @@ -361,8 +361,13 @@ If the values are not strictly equal, an `AssertionError` is thrown with a

## assert.throws(block[, error][, message])

Expects the function `block` to throw an error. If specified, `error` can be a
constructor, [`RegExp`][], or validation function.
Expects the function `block` to throw an error.

If specified, `error` can be a constructor, [`RegExp`][], or validation
function.

If specified, `message` will be the message provided by the `AssertionError` if
the block fails to throw.

Validate instanceof using constructor:

Expand Down Expand Up @@ -402,6 +407,18 @@ assert.throws(
);
```

Note that `error` can not be a string. If a string is provided as the second
argument, then `error` is assumed to be omitted and the string will be used for
`message` instead. This can lead to easy-to-miss mistakes:

```js
// THIS IS A MISTAKE! DO NOT DO THIS!
assert.throws(myFunction, 'missing foo', 'did not throw with expected message');

// Do this instead.
assert.throws(myFunction, /missing foo/, 'did not throw with expected message');
```

[Locked]: documentation.html#documentation_stability_index
[`assert.deepEqual()`]: #assert_assert_deepequal_actual_expected_message
[`assert.deepStrictEqual()`]: #assert_assert_deepstrictequal_actual_expected_message
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