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# Enforce valid `describe()` callback (`valid-describe-callback`)
Using an improper `describe()` callback function can lead to unexpected test
errors.
## Rule Details
This rule validates that the second parameter of a `describe()` function is a
callback function. This callback function:
- should not be
[async](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function)
- should not contain any parameters
- should not contain any `return` statements
The following `describe` function aliases are also validated:
- `describe`
- `describe.only`
- `describe.skip`
- `fdescribe`
- `xdescribe`
The following patterns are considered warnings:
```js
// Async callback functions are not allowed
describe('myFunction()', async () => {
// ...
});
// Callback function parameters are not allowed
describe('myFunction()', done => {
// ...
});
//
describe('myFunction', () => {
// No return statements are allowed in block of a callback function
return Promise.resolve().then(() => {
it('breaks', () => {
throw new Error('Fail');
});
});
});
// Returning a value from a describe block is not allowed
describe('myFunction', () =>
it('returns a truthy value', () => {
expect(myFunction()).toBeTruthy();
}));
```
The following patterns are not considered warnings:
```js
describe('myFunction()', () => {
it('returns a truthy value', () => {
expect(myFunction()).toBeTruthy();
});
});
```