# vitest/prefer-to-be

> Require `toBe()` for primitive literals, and `toBeNull()`, `toBeUndefined()`, `toBeNaN()`

`toEqual()` and `toStrictEqual()` compare objects property by property. For a string, a number or a boolean they do the same check as `toBe()`, and `toBe()` tells the reader that one plain value is expected. `null`, `undefined` and `NaN` have matchers that name the value.

| Written | Use instead |
| --- | --- |
| `toEqual(2)`, `toStrictEqual("config")` | `toBe(2)`, `toBe("config")` |
| `toBe(null)`, `toEqual(null)` | `toBeNull()` |
| `toBe(undefined)`, `not.toBeDefined()` | `toBeUndefined()` |
| `not.toBe(undefined)`, `not.toBeUndefined()` | `toBeDefined()` |
| `toBe(NaN)`, `toEqual(NaN)` | `toBeNaN()` |

`--fix` rewrites the matcher.

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. To turn it on:

```toml bunfig.toml
[lint.rules]
"vitest/prefer-to-be" = "error" # or "warn"
```

{/* End of the generated section. */}

## Examples

Reported:

{/* bad {"count": 7} */}
```ts
import { expect, test } from "vitest";

test("parses the header", () => {
  expect(header.version).toEqual(2);
  expect(header.name).toStrictEqual("config");
  expect(header.parent).toBe(null);
  expect(header.comment).not.toBeDefined();
  expect(header.size).not.toBe(undefined);
  expect(header.date).not.toBeUndefined();
  expect(header.ratio).toEqual(NaN);
});
```

Not reported:

{/* good */}
```ts
import { expect, test } from "vitest";

test("parses the header", () => {
  expect(header.version).toBe(2);
  expect(header.name).toBe("config");
  expect(header.parent).toBeNull();
  expect(header.comment).toBeUndefined();
  expect(header.size).toBeDefined();
  expect(header.date).toBeDefined();
  expect(header.ratio).toBeNaN();
});
```

Only literals count. The rule ignores objects, arrays and variables:

{/* good */}
```ts
import { expect, test } from "vitest";

test("parses the body", () => {
  expect(body.tags).toEqual(["a", "b"]);
  expect(body.length).toEqual(expectedLength);
});
```