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Rslint

    valid-expect-with-promise

    Added in v0.9.4

    Configuration

    rslint.config.ts
    import { defineConfig, jestPlugin } from '@rslint/core';

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

    Rule Details

    Require that resolves and rejects modifiers are present (and only) for promise-like types.

    When working with promises, you must remember to use resolves and rejects to assert on the value returned (or thrown) by the promise, rather than the promise itself. Inversely, while Jest does not prevent you from using resolves and rejects on non-promise values, it is not necessary.

    This rule requires type information and reports when:

    • an expect is given a promise-like value but without resolves or rejects
    • an expect is not given a promise-like value, but is used with resolves or rejects

    Examples of incorrect code for this rule:

    expect('hello world').resolves.toBe('hello sunshine');

expect(new Promise(r => r(0))).toThrow('oh noes!');

    Examples of correct code for this rule:

    expect('hello world').toBe('hello sunshine');

expect(new Promise(r => r(0))).rejects.toThrow('oh noes!');

    Options

    • First argument (optional): object with checkThenables
      • checkThenables: also treat values whose then method accepts both a fulfillment and a rejection callback as promises, not just Promise itself. Default is false.

    A thenable is an object with a then method, such as a Promise, TypeScript's built-in PromiseLike interface, or any custom object that has a .then(). This option is useful when working with older Promise polyfills instead of the native Promise class, or when the global Promise is not declared by TypeScript's default libraries.

    Examples of incorrect code with { "checkThenables": true }:

    { "jest/valid-expect-with-promise": ["error", { "checkThenables": true }] }
    declare function createPromiseLike(): PromiseLike<string>;

expect(createPromiseLike()).toBe('hello sunshine');

interface MyThenable {
  then(onFulfilled: () => void, onRejected: () => void): MyThenable;
}

declare function createMyThenable(): MyThenable;

expect(createMyThenable()).toBe('hello sunshine');

    Examples of correct code with { "checkThenables": true }:

    { "jest/valid-expect-with-promise": ["error", { "checkThenables": true }] }
    declare function createPromiseLike(): PromiseLike<string>;

await expect(createPromiseLike()).resolves.toBe('hello sunshine');

interface MyThenable {
  then(onFulfilled: () => void, onRejected: () => void): MyThenable;
}

declare function createMyThenable(): MyThenable;

await expect(createMyThenable()).resolves.toBe('hello sunshine');

    Original Documentation