---
url: /docs/guide/usage/linter/rules/jest/prefer-ending-with-an-expect.md
---

### What it does

Enforces that test blocks end with an assertion (`expect` or a configured
assertion function).

### Why is this bad?

A test that doesn't end with an assertion may be performing side effects
or setup after its last check, which makes the test harder to understand
and can hide failures. Ending with an assertion ensures the test's final
action is verifying behavior.

### Examples

Examples of **incorrect** code for this rule with default values:

```js
it("lets me change the selected option", () => {
  const container = render(MySelect, {
    props: { options: [1, 2, 3], selected: 1 },
  });

  expect(container).toBeDefined();
  expect(container.toHTML()).toContain('<option value="1" selected>');

  container.setProp("selected", 2);
});
```

Examples of **correct** code for this rule with defaults values:

```js
it("lets me change the selected option", () => {
  const container = render(MySelect, {
    props: { options: [1, 2, 3], selected: 1 },
  });

  expect(container).toBeDefined();
  expect(container.toHTML()).toContain('<option value="1" selected>');

  container.setProp("selected", 2);

  expect(container.toHTML()).not.toContain('<option value="1" selected>');
  expect(container.toHTML()).toContain('<option value="2" selected>');
});
```

Examples of **incorrect** code for this rule with `{ "assertFunctionNames": ["expect"] }`:

```js
import { expectSaga } from "redux-saga-test-plan";
import { addSaga } from "../src/sagas";

test("returns sum", () => {
  expectSaga(addSaga, 1, 1).returns(2).run();
});
```

Examples of **correct** code for this rule with `{ "assertFunctionNames": ["expect"] }`:

```js
import { expectSaga } from "redux-saga-test-plan";
import { addSaga } from "../src/sagas";

test("returns sum", () => {
  expectSaga(addSaga, 1, 1).returns(2).run();
});
```

Examples of **correct** code for this rule with `{ "additionalTestBlockFunctions": ["each.test"] }`:

```js
each([
  [2, 3],
  [1, 3],
]).test("the selection can change from %d to %d", (firstSelection, secondSelection) => {
  const container = render(MySelect, {
    props: { options: [1, 2, 3], selected: firstSelection },
  });

  expect(container).toBeDefined();
  expect(container.toHTML()).toContain(`<option value="${firstSelection}" selected>`);

  container.setProp("selected", secondSelection);

  expect(container.toHTML()).not.toContain(`<option value="${firstSelection}" selected>`);
  expect(container.toHTML()).toContain(`<option value="${secondSelection}" selected>`);
});
```

## Configuration

This rule accepts a configuration object with the following properties:

### additionalTestBlockFunctions

type: `string[]`

default: `[]`

An array of function names that should also be treated as test blocks.

### assertFunctionNames

type: `string[]`

A list of function names that should be treated as assertion functions.
Default: `["expect"]`

## How to use

## Version

This rule was added in v1.60.0.

## References