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[readme] improve t.throws/t.doesNotThrow documentation
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* Described method behavior when "expected" parameter is a string.

* `throws`: Described method behavior when "expected" parameter is an object (i.e. validation object).

* Added usage example for when expected parameter is a regex.

Fixes #540.
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cagross authored and ljharb committed Jan 18, 2021
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Showing 1 changed file with 5 additions and 2 deletions.
7 changes: 5 additions & 2 deletions readme.markdown
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Expand Up @@ -286,12 +286,15 @@ Aliases: `t.notLooseEqual()`, `t.notLooseEquals()`

## t.throws(fn, expected, msg)

Assert that the function call `fn()` throws an exception. `expected`, if present, must be a `RegExp` or `Function`. The `RegExp` matches the string representation of the exception, as generated by `err.toString()`. The `Function` is the exception thrown (e.g. `Error`). `msg` is an optional description of the assertion.
Assert that the function call `fn()` throws an exception. `expected`, if present, must be a `RegExp`, `Function`, or `Object`. The `RegExp` matches the string representation of the exception, as generated by `err.toString()`. For example, if you set `expected` to `/user/`, the test will pass only if the string representation of the exception contains the word `user`. Any other exception will result in a failed test. The `Function` is the exception thrown (e.g. `Error`). `Object` in this case corresponds to a so-called validation object, in which each property is tested for strict deep equality. This is very similar to how Node's `assert.throws()` method tests validation objects (please see the [Node _assert.throws()_ documentation](https://nodejs.org/api/assert.html#assert_assert_throws_fn_error_message) for an example). If `expected` is not of type `RegExp`, `Function`, or `Object`, or omitted entirely, any exception will result in a passed test. `msg` is an optional description of the assertion.

Please note that the second parameter, `expected`, cannot be of type `string`. If a value of type `string` is provided for `expected`, then `t.throws(fn, expected, msg)` will execute, but the value of `expected` will be set to `undefined`, and the specified string will be set as the value for the `msg` parameter (regardless of what _actually_ passed as the third parameter). This can cause unexpected results, so please be mindful.

## t.doesNotThrow(fn, expected, msg)

Assert that the function call `fn()` does not throw an exception. `expected`, if present, limits what should not be thrown. For example, set `expected` to `/user/` to fail the test only if the string representation of the exception contains the word `user`. Any other exception would pass the test. If `expected` is omitted, any exception will fail the test. `msg` is an optional description of the assertion.
Assert that the function call `fn()` does not throw an exception. `expected`, if present, limits what should not be thrown, and must be a `RegExp` or `Function`. The `RegExp` matches the string representation of the exception, as generated by `err.toString()`. For example, if you set `expected` to `/user/`, the test will fail only if the string representation of the exception contains the word `user`. Any other exception will result in a passed test. The `Function` is the exception thrown (e.g. `Error`). If `expected` is not of type `RegExp` or `Function`, or omitted entirely, any exception will result in a failed test. `msg` is an optional description of the assertion.

Please note that the second parameter, `expected`, cannot be of type `string`. If a value of type `string` is provided for `expected`, then `t.doesNotThrows(fn, expected, msg)` will execute, but the value of `expected` will be set to `undefined`, and the specified string will be set as the value for the `msg` parameter (regardless of what _actually_ passed as the third parameter). This can cause unexpected results, so please be mindful.
## t.test(name, [opts], cb)

Create a subtest with a new test handle `st` from `cb(st)` inside the current test `t`. `cb(st)` will only fire when `t` finishes. Additional tests queued up after `t` will not be run until all subtests finish.
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