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# valid-expect-with-promise

[Added in v0.9.3](https://github.com/web-infra-dev/rslint/releases/tag/v0.9.3)
## Configuration

| Preset                     | Configured Value |
| -------------------------- | ---------------- |
| ✅ rstestPlugin.configs.all | `"warn"`         |


```ts title=rslint.config.ts
import { defineConfig, rstestPlugin } from '@rslint/core';

export default defineConfig([
  rstestPlugin.configs.recommended,
  {
    rules: {
      'rstest/valid-expect-with-promise': 'error',
    },
  },
]);
```

## Rule Details

Requires assertions on Promise values to use `resolves` or `rejects`, and reports those modifiers when the subject is not a Promise. This prevents an assertion from inspecting the Promise object itself and catches promise modifiers that would fail at runtime. The rule uses TypeScript type information and distinguishes Promise instances from Promise constructors.

Ordinary `expect` and `expect.soft` assertions are checked, including Chai-style chains and promise modifiers between Chai assertions. When a direct Chai `property` assertion changes the current subject, the rule checks the statically named property's type. It skips subject-changing chains that cannot be resolved statically. Global expect calls, imports and aliases from Rstest modules, `import.meta.rstest`, and test-context expect calls are recognized. `expect.poll` and `expect.element` are excluded because they have their own asynchronous assertion semantics.

Rstest calls a function passed to `expect(...).rejects` without arguments. The rule therefore requires an applicable zero-argument signature and checks its return type. A function whose zero-argument call returns a Promise is valid with `rejects`; a function that requires arguments is reported even when its declared return type is a Promise. A Promise-returning function used with `resolves` is still a function subject and is also reported. See the [Rstest expect API](https://rstest.rs/api/runtime-api/test-api/expect) for Promise, soft, polling, and browser-element assertions.

## Incorrect

```ts
test('loads the current user', async () => {
  expect(loadCurrentUser()).toMatchObject({ name: 'Ada' });

  await expect({ name: 'Ada' }).resolves.toMatchObject({ name: 'Ada' });
});

test('rejects invalid credentials', async () => {
  await expect(() => validateCredentials()).rejects.toThrow();
});
```

## Correct

```ts
test('loads the current user', async () => {
  await expect(loadCurrentUser()).resolves.toMatchObject({ name: 'Ada' });

  expect({ name: 'Ada' }).toMatchObject({ name: 'Ada' });
});

test('rejects invalid credentials', async () => {
  await expect(() => validateCredentialsAsync()).rejects.toThrow();
});
```

## Options

```json
{
  "rstest/valid-expect-with-promise": [
    "error",
    {
      "checkThenables": true
    }
  ]
}
```

| Option           | Type      | Default | Description                                                                                          |
| ---------------- | --------- | ------- | ---------------------------------------------------------------------------------------------------- |
| `checkThenables` | `boolean` | `false` | Treat values whose `then` method accepts both fulfillment and rejection callbacks as Promise values. |