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# Enforce valid `expect()` usage (`valid-expect`)
Ensure `expect()` is called with a single argument and there is an actual
expectation made.
## Rule details
This rule triggers a warning if `expect()` is called with more than one argument
or without arguments. It would also issue a warning if there is nothing called
on `expect()`, e.g.:
```js
expect();
expect('something');
```
or when a matcher function was not called, e.g.:
```js
expect(true).toBeDefined;
```
or when an async assertion was not `await`ed or returned, e.g.:
```js
expect(Promise.resolve('Hi!')).resolves.toBe('Hi!');
```
This rule is enabled by default.
## Options
```json5
{
type: 'object',
properties: {
alwaysAwait: {
type: 'boolean',
default: false,
},
asyncMatchers: {
type: 'array',
items: { type: 'string' },
default: ['toResolve', 'toReject'],
},
minArgs: {
type: 'number',
minimum: 1,
},
maxArgs: {
type: 'number',
minimum: 1,
},
},
additionalProperties: false,
}
```
### `alwaysAwait`
Enforces to use `await` inside block statements. Using `return` will trigger a
warning. Returning one line statements with arrow functions is _always allowed_.
Examples of **incorrect** code for the { "alwaysAwait": **true** } option:
```js
// alwaysAwait: true
test('test1', async () => {
await expect(Promise.resolve(2)).resolves.toBeDefined();
return expect(Promise.resolve(1)).resolves.toBe(1); // `return` statement will trigger a warning
});
```
Examples of **correct** code for the { "alwaysAwait": **true** } option:
```js
// alwaysAwait: true
test('test1', async () => {
await expect(Promise.resolve(2)).resolves.toBeDefined();
await expect(Promise.resolve(1)).resolves.toBe(1);
});
test('test2', () => expect(Promise.resolve(2)).resolves.toBe(2));
```
### `asyncMatchers`
Allows specifying which matchers return promises, and so should be considered
async when checking if an `expect` should be returned or awaited.
By default, this has a list of all the async matchers provided by
`jest-extended` (namely, `toResolve` and `toReject`).
### `minArgs` & `maxArgs`
Enforces the minimum and maximum number of arguments that `expect` can take, and
is required to take.
Both of these properties have a default value of `1`, which is the number of
arguments supported by vanilla `expect`.
This is useful when you're using libraries that increase the number of arguments
supported by `expect`, such as
[`jest-expect-message`](https://www.npmjs.com/package/jest-expect-message).
### Default configuration
The following patterns are considered warnings:
```js
test('all the things', async () => {
expect();
expect().toEqual('something');
expect('something', 'else');
expect('something');
await expect('something');
expect(true).toBeDefined;
expect(Promise.resolve('hello')).resolves;
expect(Promise.resolve('hello')).resolves.toEqual('hello');
Promise.resolve(expect(Promise.resolve('hello')).resolves.toEqual('hello'));
Promise.all([
expect(Promise.resolve('hello')).resolves.toEqual('hello'),
expect(Promise.resolve('hi')).resolves.toEqual('hi'),
]);
});
```
The following patterns are not warnings:
```js
test('all the things', async () => {
expect('something').toEqual('something');
expect([1, 2, 3]).toEqual([1, 2, 3]);
expect(true).toBeDefined();
await expect(Promise.resolve('hello')).resolves.toEqual('hello');
await Promise.resolve(
expect(Promise.resolve('hello')).resolves.toEqual('hello'),
);
await Promise.all(
expect(Promise.resolve('hello')).resolves.toEqual('hello'),
expect(Promise.resolve('hi')).resolves.toEqual('hi'),
);
});
```