feat: add prefer-partially-checked rule

Suggest toBePartiallyChecked() instead of
toHaveAttribute('aria-checked', 'mixed'). Fills a pre-existing
gap—the matcher has been in jest-dom for years without a
corresponding lint rule.

Author: shamrt-v

docs/rules/prefer-partially-checked.md

@@ -0,0 +1,44 @@
+# Prefer toBePartiallyChecked over checking attributes (`jest-dom/prefer-partially-checked`)
+
+💼 This rule is enabled in the ✅ `recommended` config.
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+## Rule Details
+
+This rule suggests using `toBePartiallyChecked()` instead of checking for the
+`"mixed"` value of the `aria-checked` attribute with `.toHaveAttribute()` or
+`.toHaveProperty()`. This improves readability and ensures you are using the
+semantically correct jest-dom matcher.
+
+Examples of **incorrect** code for this rule:
+
+```js
+expect(element).toHaveAttribute("aria-checked", "mixed");
+expect(element).toHaveProperty("aria-checked", "mixed");
+expect(element).not.toHaveAttribute("aria-checked", "mixed");
+```
+
+Examples of **correct** code for this rule:
+
+```js
+expect(element).toBePartiallyChecked();
+
+expect(element).not.toBePartiallyChecked();
+
+expect(element).toHaveAttribute("aria-checked", "true");
+expect(element).toHaveAttribute("aria-checked", "false");
+```
+
+## When Not To Use It
+
+Don't use this rule if you:
+
+- don't use `jest-dom`
+- want to allow `.toHaveAttribute()` and `.toHaveProperty()` for `aria-checked="mixed"`
+
+## Further Reading
+
+- [jest-dom `toBePartiallyChecked`](https://github.com/testing-library/jest-dom#tobepartiallychecked)

src/__tests__/lib/rules/prefer-partially-checked.js

@@ -0,0 +1,90 @@
+/**
+ * @fileoverview prefer toBePartiallyChecked over checking aria-checked for mixed state
+ */
+
+import { RuleTester } from "eslint";
+import * as rule from "../../../rules/prefer-partially-checked";
+
+const ruleTester = new RuleTester({
+  parserOptions: { ecmaVersion: 2015, sourceType: "module" },
+});
+
+ruleTester.run("prefer-partially-checked", rule, {
+  valid: [
+    `expect(element).toBePartiallyChecked()`,
+    `expect(element).not.toBePartiallyChecked()`,
+    `const el = screen.getByText("foo"); expect(el).toBePartiallyChecked()`,
+    `const el = screen.getByText("foo"); expect(el).toHaveAttribute("aria-checked", "true")`,
+    `const el = screen.getByText("foo"); expect(el).toHaveAttribute("aria-checked", "false")`,
+    `const el = screen.getByText("foo"); expect(el).toHaveAttribute("aria-checked")`,
+    `const el = screen.getByText("foo"); expect(el).toHaveProperty("aria-checked", "true")`,
+    `const el = screen.getByText("foo"); expect(el).not.toHaveAttribute("aria-checked")`,
+    `const el = foo.bar(); expect(el).toHaveAttribute("aria-checked", "mixed")`,
+    `const el = foo.bar(); expect(el).toHaveProperty("aria-checked", "mixed")`,
+  ],
+  invalid: [
+    {
+      code: `const el = screen.getByText("foo"); expect(el).toHaveAttribute("aria-checked", "mixed")`,
+      errors: [
+        {
+          message: `Use toBePartiallyChecked() instead of toHaveAttribute('aria-checked', 'mixed')`,
+        },
+      ],
+      output: `const el = screen.getByText("foo"); expect(el).toBePartiallyChecked()`,
+    },
+    {
+      code: `const el = screen.getByText("foo"); expect(el).toHaveProperty("aria-checked", "mixed")`,
+      errors: [
+        {
+          message: `Use toBePartiallyChecked() instead of toHaveProperty('aria-checked', 'mixed')`,
+        },
+      ],
+      output: `const el = screen.getByText("foo"); expect(el).toBePartiallyChecked()`,
+    },
+    {
+      code: `expect(getByText("foo")).toHaveAttribute("aria-checked", "mixed")`,
+      errors: [
+        {
+          message: `Use toBePartiallyChecked() instead of toHaveAttribute('aria-checked', 'mixed')`,
+        },
+      ],
+      output: `expect(getByText("foo")).toBePartiallyChecked()`,
+    },
+    {
+      code: `expect(getByRole("checkbox")).toHaveAttribute("aria-checked", "mixed")`,
+      errors: [
+        {
+          message: `Use toBePartiallyChecked() instead of toHaveAttribute('aria-checked', 'mixed')`,
+        },
+      ],
+      output: `expect(getByRole("checkbox")).toBePartiallyChecked()`,
+    },
+    {
+      code: `const el = screen.getByText("foo"); expect(el).not.toHaveAttribute("aria-checked", "mixed")`,
+      errors: [
+        {
+          message: `Use not.toBePartiallyChecked() instead of not.toHaveAttribute('aria-checked', 'mixed')`,
+        },
+      ],
+      output: `const el = screen.getByText("foo"); expect(el).not.toBePartiallyChecked()`,
+    },
+    {
+      code: `const el = screen.getByText("foo"); expect(el).not.toHaveProperty("aria-checked", "mixed")`,
+      errors: [
+        {
+          message: `Use not.toBePartiallyChecked() instead of not.toHaveProperty('aria-checked', 'mixed')`,
+        },
+      ],
+      output: `const el = screen.getByText("foo"); expect(el).not.toBePartiallyChecked()`,
+    },
+    {
+      code: `expect(getByText("foo")).not.toHaveAttribute("aria-checked", "mixed")`,
+      errors: [
+        {
+          message: `Use not.toBePartiallyChecked() instead of not.toHaveAttribute('aria-checked', 'mixed')`,
+        },
+      ],
+      output: `expect(getByText("foo")).not.toBePartiallyChecked()`,
+    },
+  ],
+});

src/rules/prefer-partially-checked.js

@@ -0,0 +1,21 @@
+/**
+ * @fileoverview prefer toBePartiallyChecked over checking aria-checked for mixed state
+ */
+
+import createPartiallyBannedAttributeRule from "../createPartiallyBannedAttributeRule";
+
+export const meta = {
+  docs: {
+    description:
+      "prefer toBePartiallyChecked over checking aria-checked attribute for mixed state",
+    category: "Best Practices",
+    recommended: true,
+    url: "prefer-partially-checked",
+  },
+  fixable: "code",
+};
+
+export const create = createPartiallyBannedAttributeRule({
+  preferred: "toBePartiallyChecked",
+  attribute: "aria-checked",
+});