#prefer-to-be

#Configuration

import { defineConfig, rstestPlugin } from '@rslint/core';

export default defineConfig([
  rstestPlugin.configs.recommended,
  {
    rules: {
      'rstest/prefer-to-be': 'error',
    },
  },
]);

#Rule Details

This rule asks equality assertions to use the matcher that most directly states what is being checked. Primitive literals use toBe(), while null, undefined and NaN use their dedicated matchers. Negated undefined checks are normalized to the positive complementary matcher.

Examples of incorrect code for this rule:

expect(status).toEqual('ready');
expect(result).toStrictEqual(1);
expect(value).toBe(null);
expect(value).not.toEqual(undefined);
expect(value).toStrictEqual(NaN);

Examples of correct code for this rule:

expect(status).toBe('ready');
expect(result).toBe(1);
expect(value).toBeNull();
expect(value).toBeDefined();
expect(value).toBeNaN();

expect(result).toEqual({ value: 1 });
expect(total).toBeCloseTo(0.3);

Fractional numeric literals are left alone. Rstest uses Vitest's assertion implementation, whose public API recommends toBeCloseTo() for floating-point comparisons; automatically changing toEqual(0.3) to toBe(0.3) would preserve exact equality while steering the test toward the wrong matcher.

The rule recognizes Rstest globals, imports from Rstest packages, namespace and require bindings, import.meta.rstest, expect.soft(), expect.poll(), and the expect supplied by a test context. Browser-only expect.element() assertions are excluded because their matcher set does not provide these value matchers. Chai-style assertions such as expect(value).to.equal(1) are also left alone. Locally declared values named undefined or NaN do not select the dedicated built-in matchers.

#Autofix

The autofix renames the matcher, removes arguments from dedicated no-argument matchers, and removes .not when a negated undefined check is rewritten to its positive complement. The authored accessor style is retained, so ["toEqual"] becomes ["toBe"]. If removing arguments would delete a comment, the diagnostic is emitted without a fix.