Docs: prefer-output-null

Author: aladdin-add

README.md

@@ -53,6 +53,7 @@ Name | ✔️ | 🛠 | Description
 [no-identical-tests](https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/master/docs/rules/no-identical-tests.md) | | 🛠 | Disallows identical tests
 [no-missing-placeholders](https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/master/docs/rules/no-missing-placeholders.md) | ✔️ | | Disallows missing placeholders in rule report messages
 [no-useless-token-range](https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/master/docs/rules/no-useless-token-range.md) | ✔️ | 🛠 | Disallows unnecessary calls to sourceCode.getFirstToken and sourceCode.getLastToken
+[prefer-output-null](https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/master/docs/rules/prefer-output-null.md) | | | Disallows invalid RuleTester test cases with the output the same as the code.
 [prefer-placeholders](https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/master/docs/rules/prefer-placeholders.md) | | | Disallows template literals as report messages
 [report-message-format](https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/master/docs/rules/report-message-format.md) | | | Enforces a consistent format for report messages
 [require-meta-fixable](https://github.com/not-an-aardvark/eslint-plugin-eslint-plugin/blob/master/docs/rules/require-meta-fixable.md) | ✔️ | | Requires a `meta.fixable` property for fixable rules

docs/rules/prefer-output-null.md

@@ -0,0 +1,31 @@
+# Disallows invalid RuleTester test cases with the output the same as the code. (prefer-output-null)
+
+## Rule Details
+
+This rule aims to enforce `output: null` for invalid test cases to indicate that no output is produced.
+
+Examples of **incorrect** code for this rule:
+
+```js
+/* eslint eslint-plugin/prefer-output-null: error */
+
+new RuleTester().run('foo', bar, {
+    valid: [],
+    invalid: [
+      { code: 'foo', errors: [{ message: 'bar' }] },
+    ]
+});
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/* eslint eslint-plugin/prefer-output-null: error */
+
+new RuleTester().run('foo', bar, {
+    valid: [],
+    invalid: [
+      { code: 'foo', output: null, errors: [{ message: 'bar' }] },
+    ]
+});
+```