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feat: create prefer-expect-resolves rule #822

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Sep 29, 2021
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feat: create prefer-expect-resolves rule #822

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29e6820
feat: create `prefer-expect-resolves` rule
G-Rath Apr 11, 2021
1a34267
feat(prefer-expect-resolves): add fixer
G-Rath Jul 15, 2021
9b93db2
chore: readme lint
SimenB Sep 29, 2021
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89 changes: 45 additions & 44 deletions README.md
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Expand Up @@ -150,50 +150,51 @@ installations requiring long-term consistency.

<!-- begin base rules list -->

| Rule | Description | Configurations | Fixable |
| ---------------------------------------------------------------------------- | --------------------------------------------------------------- | ---------------- | ------------ |
| [consistent-test-it](docs/rules/consistent-test-it.md) | Have control over `test` and `it` usages | | ![fixable][] |
| [expect-expect](docs/rules/expect-expect.md) | Enforce assertion to be made in a test body | ![recommended][] | |
| [lowercase-name](docs/rules/lowercase-name.md) | Enforce lowercase test names | | ![fixable][] |
| [max-nested-describe](docs/rules/max-nested-describe.md) | Enforces a maximum depth to nested describe calls | | |
| [no-alias-methods](docs/rules/no-alias-methods.md) | Disallow alias methods | ![style][] | ![fixable][] |
| [no-commented-out-tests](docs/rules/no-commented-out-tests.md) | Disallow commented out tests | ![recommended][] | |
| [no-conditional-expect](docs/rules/no-conditional-expect.md) | Prevent calling `expect` conditionally | ![recommended][] | |
| [no-deprecated-functions](docs/rules/no-deprecated-functions.md) | Disallow use of deprecated functions | ![recommended][] | ![fixable][] |
| [no-disabled-tests](docs/rules/no-disabled-tests.md) | Disallow disabled tests | ![recommended][] | |
| [no-done-callback](docs/rules/no-done-callback.md) | Avoid using a callback in asynchronous tests and hooks | ![recommended][] | ![suggest][] |
| [no-duplicate-hooks](docs/rules/no-duplicate-hooks.md) | Disallow duplicate setup and teardown hooks | | |
| [no-export](docs/rules/no-export.md) | Disallow using `exports` in files containing tests | ![recommended][] | |
| [no-focused-tests](docs/rules/no-focused-tests.md) | Disallow focused tests | ![recommended][] | ![suggest][] |
| [no-hooks](docs/rules/no-hooks.md) | Disallow setup and teardown hooks | | |
| [no-identical-title](docs/rules/no-identical-title.md) | Disallow identical titles | ![recommended][] | |
| [no-if](docs/rules/no-if.md) | Disallow conditional logic | | |
| [no-interpolation-in-snapshots](docs/rules/no-interpolation-in-snapshots.md) | Disallow string interpolation inside snapshots | ![recommended][] | |
| [no-jasmine-globals](docs/rules/no-jasmine-globals.md) | Disallow Jasmine globals | ![recommended][] | ![fixable][] |
| [no-jest-import](docs/rules/no-jest-import.md) | Disallow importing Jest | ![recommended][] | |
| [no-large-snapshots](docs/rules/no-large-snapshots.md) | disallow large snapshots | | |
| [no-mocks-import](docs/rules/no-mocks-import.md) | Disallow manually importing from `__mocks__` | ![recommended][] | |
| [no-restricted-matchers](docs/rules/no-restricted-matchers.md) | Disallow specific matchers & modifiers | | |
| [no-standalone-expect](docs/rules/no-standalone-expect.md) | Disallow using `expect` outside of `it` or `test` blocks | ![recommended][] | |
| [no-test-prefixes](docs/rules/no-test-prefixes.md) | Use `.only` and `.skip` over `f` and `x` | ![recommended][] | ![fixable][] |
| [no-test-return-statement](docs/rules/no-test-return-statement.md) | Disallow explicitly returning from tests | | |
| [prefer-called-with](docs/rules/prefer-called-with.md) | Suggest using `toBeCalledWith()` or `toHaveBeenCalledWith()` | | |
| [prefer-expect-assertions](docs/rules/prefer-expect-assertions.md) | Suggest using `expect.assertions()` OR `expect.hasAssertions()` | | ![suggest][] |
| [prefer-hooks-on-top](docs/rules/prefer-hooks-on-top.md) | Suggest having hooks before any test cases | | |
| [prefer-spy-on](docs/rules/prefer-spy-on.md) | Suggest using `jest.spyOn()` | | ![fixable][] |
| [prefer-strict-equal](docs/rules/prefer-strict-equal.md) | Suggest using `toStrictEqual()` | | ![suggest][] |
| [prefer-to-be](docs/rules/prefer-to-be.md) | Suggest using `toBe()` for primitive literals | | ![fixable][] |
| [prefer-to-be-null](docs/rules/prefer-to-be-null.md) | Suggest using `toBeNull()` | ![style][] | ![fixable][] |
| [prefer-to-be-undefined](docs/rules/prefer-to-be-undefined.md) | Suggest using `toBeUndefined()` | ![style][] | ![fixable][] |
| [prefer-to-contain](docs/rules/prefer-to-contain.md) | Suggest using `toContain()` | ![style][] | ![fixable][] |
| [prefer-to-have-length](docs/rules/prefer-to-have-length.md) | Suggest using `toHaveLength()` | ![style][] | ![fixable][] |
| [prefer-todo](docs/rules/prefer-todo.md) | Suggest using `test.todo` | | ![fixable][] |
| [require-to-throw-message](docs/rules/require-to-throw-message.md) | Require a message for `toThrow()` | | |
| [require-top-level-describe](docs/rules/require-top-level-describe.md) | Require test cases and hooks to be inside a `describe` block | | |
| [valid-describe](docs/rules/valid-describe.md) | Enforce valid `describe()` callback | ![recommended][] | |
| [valid-expect](docs/rules/valid-expect.md) | Enforce valid `expect()` usage | ![recommended][] | |
| [valid-expect-in-promise](docs/rules/valid-expect-in-promise.md) | Enforce having return statement when testing with promises | ![recommended][] | |
| [valid-title](docs/rules/valid-title.md) | Enforce valid titles | ![recommended][] | ![fixable][] |
| Rule | Description | Configurations | Fixable |
| ---------------------------------------------------------------------------- | ------------------------------------------------------------------- | ---------------- | ------------ |
| [consistent-test-it](docs/rules/consistent-test-it.md) | Have control over `test` and `it` usages | | ![fixable][] |
| [expect-expect](docs/rules/expect-expect.md) | Enforce assertion to be made in a test body | ![recommended][] | |
| [lowercase-name](docs/rules/lowercase-name.md) | Enforce lowercase test names | | ![fixable][] |
| [max-nested-describe](docs/rules/max-nested-describe.md) | Enforces a maximum depth to nested describe calls | | |
| [no-alias-methods](docs/rules/no-alias-methods.md) | Disallow alias methods | ![style][] | ![fixable][] |
| [no-commented-out-tests](docs/rules/no-commented-out-tests.md) | Disallow commented out tests | ![recommended][] | |
| [no-conditional-expect](docs/rules/no-conditional-expect.md) | Prevent calling `expect` conditionally | ![recommended][] | |
| [no-deprecated-functions](docs/rules/no-deprecated-functions.md) | Disallow use of deprecated functions | ![recommended][] | ![fixable][] |
| [no-disabled-tests](docs/rules/no-disabled-tests.md) | Disallow disabled tests | ![recommended][] | |
| [no-done-callback](docs/rules/no-done-callback.md) | Avoid using a callback in asynchronous tests and hooks | ![recommended][] | ![suggest][] |
| [no-duplicate-hooks](docs/rules/no-duplicate-hooks.md) | Disallow duplicate setup and teardown hooks | | |
| [no-export](docs/rules/no-export.md) | Disallow using `exports` in files containing tests | ![recommended][] | |
| [no-focused-tests](docs/rules/no-focused-tests.md) | Disallow focused tests | ![recommended][] | ![suggest][] |
| [no-hooks](docs/rules/no-hooks.md) | Disallow setup and teardown hooks | | |
| [no-identical-title](docs/rules/no-identical-title.md) | Disallow identical titles | ![recommended][] | |
| [no-if](docs/rules/no-if.md) | Disallow conditional logic | | |
| [no-interpolation-in-snapshots](docs/rules/no-interpolation-in-snapshots.md) | Disallow string interpolation inside snapshots | ![recommended][] | |
| [no-jasmine-globals](docs/rules/no-jasmine-globals.md) | Disallow Jasmine globals | ![recommended][] | ![fixable][] |
| [no-jest-import](docs/rules/no-jest-import.md) | Disallow importing Jest | ![recommended][] | |
| [no-large-snapshots](docs/rules/no-large-snapshots.md) | disallow large snapshots | | |
| [no-mocks-import](docs/rules/no-mocks-import.md) | Disallow manually importing from `__mocks__` | ![recommended][] | |
| [no-restricted-matchers](docs/rules/no-restricted-matchers.md) | Disallow specific matchers & modifiers | | |
| [no-standalone-expect](docs/rules/no-standalone-expect.md) | Disallow using `expect` outside of `it` or `test` blocks | ![recommended][] | |
| [no-test-prefixes](docs/rules/no-test-prefixes.md) | Use `.only` and `.skip` over `f` and `x` | ![recommended][] | ![fixable][] |
| [no-test-return-statement](docs/rules/no-test-return-statement.md) | Disallow explicitly returning from tests | | |
| [prefer-called-with](docs/rules/prefer-called-with.md) | Suggest using `toBeCalledWith()` or `toHaveBeenCalledWith()` | | |
| [prefer-expect-assertions](docs/rules/prefer-expect-assertions.md) | Suggest using `expect.assertions()` OR `expect.hasAssertions()` | | ![suggest][] |
| [prefer-expect-resolves](docs/rules/prefer-expect-resolves.md) | Prefer `await expect(...).resolves` over `expect(await ...)` syntax | | ![fixable][] |
| [prefer-hooks-on-top](docs/rules/prefer-hooks-on-top.md) | Suggest having hooks before any test cases | | |
| [prefer-spy-on](docs/rules/prefer-spy-on.md) | Suggest using `jest.spyOn()` | | ![fixable][] |
| [prefer-strict-equal](docs/rules/prefer-strict-equal.md) | Suggest using `toStrictEqual()` | | ![suggest][] |
| [prefer-to-be](docs/rules/prefer-to-be.md) | Suggest using `toBe()` for primitive literals | | ![fixable][] |
| [prefer-to-be-null](docs/rules/prefer-to-be-null.md) | Suggest using `toBeNull()` | ![style][] | ![fixable][] |
| [prefer-to-be-undefined](docs/rules/prefer-to-be-undefined.md) | Suggest using `toBeUndefined()` | ![style][] | ![fixable][] |
| [prefer-to-contain](docs/rules/prefer-to-contain.md) | Suggest using `toContain()` | ![style][] | ![fixable][] |
| [prefer-to-have-length](docs/rules/prefer-to-have-length.md) | Suggest using `toHaveLength()` | ![style][] | ![fixable][] |
| [prefer-todo](docs/rules/prefer-todo.md) | Suggest using `test.todo` | | ![fixable][] |
| [require-to-throw-message](docs/rules/require-to-throw-message.md) | Require a message for `toThrow()` | | |
| [require-top-level-describe](docs/rules/require-top-level-describe.md) | Require test cases and hooks to be inside a `describe` block | | |
| [valid-describe](docs/rules/valid-describe.md) | Enforce valid `describe()` callback | ![recommended][] | |
| [valid-expect](docs/rules/valid-expect.md) | Enforce valid `expect()` usage | ![recommended][] | |
| [valid-expect-in-promise](docs/rules/valid-expect-in-promise.md) | Enforce having return statement when testing with promises | ![recommended][] | |
| [valid-title](docs/rules/valid-title.md) | Enforce valid titles | ![recommended][] | ![fixable][] |

<!-- end base rules list -->

Expand Down
53 changes: 53 additions & 0 deletions docs/rules/prefer-expect-resolves.md
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@@ -0,0 +1,53 @@
# Prefer `await expect(...).resolves` over `expect(await ...)` syntax (`prefer-expect-resolves`)

When working with promises, there are two primary ways you can test the resolved
value:

1. use the `resolve` modifier on `expect`
(`await expect(...).resolves.<matcher>` style)
2. `await` the promise and assert against its result
(`expect(await ...).<matcher>` style)

While the second style is arguably less dependent on `jest`, if the promise
rejects it will be treated as a general error, resulting in less predictable
behaviour and output from `jest`.

Additionally, favoring the first style ensures consistency with its `rejects`
counterpart, as there is no way of "awaiting" a rejection.

## Rule details

This rule triggers a warning if an `await` is done within an `expect`, and
recommends using `resolves` instead.

Examples of **incorrect** code for this rule

```js
it('passes', async () => {
expect(await someValue()).toBe(true);
});

it('is true', async () => {
const myPromise = Promise.resolve(true);

expect(await myPromise).toBe(true);
});
```

Examples of **correct** code for this rule

```js
it('passes', async () => {
await expect(someValue()).resolves.toBe(true);
});

it('is true', async () => {
const myPromise = Promise.resolve(true);

await expect(myPromise).resolves.toBe(true);
});

it('errors', async () => {
await expect(Promise.rejects('oh noes!')).rejects.toThrow('oh noes!');
});
```
1 change: 1 addition & 0 deletions src/__tests__/__snapshots__/rules.test.ts.snap
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Expand Up @@ -37,6 +37,7 @@ Object {
"jest/no-test-return-statement": "error",
"jest/prefer-called-with": "error",
"jest/prefer-expect-assertions": "error",
"jest/prefer-expect-resolves": "error",
"jest/prefer-hooks-on-top": "error",
"jest/prefer-spy-on": "error",
"jest/prefer-strict-equal": "error",
Expand Down
2 changes: 1 addition & 1 deletion src/__tests__/rules.test.ts
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Expand Up @@ -2,7 +2,7 @@ import { existsSync } from 'fs';
import { resolve } from 'path';
import plugin from '../';

const numberOfRules = 47;
const numberOfRules = 48;
const ruleNames = Object.keys(plugin.rules);
const deprecatedRules = Object.entries(plugin.rules)
.filter(([, rule]) => rule.meta.deprecated)
Expand Down
65 changes: 65 additions & 0 deletions src/rules/__tests__/prefer-expect-resolves.test.ts
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import { TSESLint } from '@typescript-eslint/experimental-utils';
import dedent from 'dedent';
import resolveFrom from 'resolve-from';
import rule from '../prefer-expect-resolves';

const ruleTester = new TSESLint.RuleTester({
parser: resolveFrom(require.resolve('eslint'), 'espree'),
parserOptions: {
ecmaVersion: 2017,
},
});

ruleTester.run('prefer-expect-resolves', rule, {
valid: [
dedent`
it('passes', async () => {
await expect(someValue()).resolves.toBe(true);
});
`,
dedent`
it('is true', async () => {
const myPromise = Promise.resolve(true);

await expect(myPromise).resolves.toBe(true);
});
`,
dedent`
it('errors', async () => {
await expect(Promise.rejects('oh noes!')).rejects.toThrow('oh noes!');
});
`,
],
invalid: [
{
code: dedent`
it('passes', async () => {
expect(await someValue()).toBe(true);
});
`,
output: dedent`
it('passes', async () => {
await expect(someValue()).resolves.toBe(true);
});
`,
errors: [{ endColumn: 27, column: 10, messageId: 'expectResolves' }],
},
{
code: dedent`
it('is true', async () => {
const myPromise = Promise.resolve(true);

expect(await myPromise).toBe(true);
});
`,
output: dedent`
it('is true', async () => {
const myPromise = Promise.resolve(true);

await expect(myPromise).resolves.toBe(true);
});
`,
errors: [{ endColumn: 25, column: 10, messageId: 'expectResolves' }],
},
],
});
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