Add testing framework

Author: JoshMock

validator/README.md

@@ -25,7 +25,7 @@ If all is well, the output will be minimal, and the process will exit cleanly.
 
 ESLint also maintains [integrations](https://eslint.org/docs/latest/use/integrations#editors) for most common code editors to provide instant inline feedback as you modify files.
 
-## Writing new linter rules
+## Writing custom rules
 
 Each rule should be written in a separate JavaScript file (e.g. `single-key-dictionary-key-is-string.js`) following the format of a custom rule [as defined by the typescript-eslint docs](https://typescript-eslint.io/developers/custom-rules).
 Within a rule's `create` function, return an object whose keys are the names of [AST node types](https://typescript-eslint.io/packages/typescript-estree/ast-spec) and whose values are functions that validate that node type.
@@ -35,6 +35,13 @@ To get a familiar the different node types possible within a TypeScript AST, pas
 
 To add your rule to the spec validator ESLint plugin, import it into [the plugin file](./eslint-plugin-es-spec.js) and add it to the `rules` object with an appropriate key.
 
+### Unit testing rules
+
+Add a file `<your rule name>.test.js` to the `test/` directory, and construct your test using the [typescript-eslint `RuleTester`](https://typescript-eslint.io/packages/rule-tester/) format.
+
+To run the entire test suite, run `npm test`.
+To run just one test file, run `npm test -- test/your-file.js`
+
 ### ESM format
 
 The validator project is written in standard JavaScript rather than TypeScript, and uses the new [ESM](https://nodejs.org/api/esm.html) module format for managing module imports and exports.

validator/package.json

@@ -5,7 +5,7 @@
   "main": "eslint-plugin-es-spec.js",
   "type": "module",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "node --import ./test/_setup.js --test"
   },
   "peerDependencies": {
     "eslint": ">=9.0.0"
@@ -15,5 +15,8 @@
   "dependencies": {
     "@typescript-eslint/utils": "^8.32.1",
     "typescript": "^5.8.3"
+  },
+  "devDependencies": {
+    "@typescript-eslint/rule-tester": "^8.32.1"
   }
 }

validator/test/_setup.js

@@ -0,0 +1,7 @@
+import * as test from 'node:test'
+import { RuleTester } from '@typescript-eslint/rule-tester'
+
+RuleTester.afterAll = test.after
+RuleTester.describe = test.describe
+RuleTester.it = test.it
+RuleTester.itOnly = test.it.only

validator/test/single-key-dictionary-key-is-string.test.js

@@ -0,0 +1,43 @@
+import { RuleTester } from '@typescript-eslint/rule-tester'
+import rule from '../rules/single-key-dictionary-key-is-string.js'
+
+const ruleTester = new RuleTester({
+  languageOptions: {
+    parserOptions: {
+      projectService: {
+        allowDefaultProject: ['*.ts*'],
+      },
+      tsconfigRootDir: import.meta.dirname,
+    },
+  },
+})
+
+ruleTester.run('single-key-dictionary-key-is-string', rule, {
+  valid: [
+    `type MyDict = SingleKeyDictionary<string, object>`,
+    `type MyDict = SingleKeyDictionary<string, any>`,
+    `type MyDict = SingleKeyDictionary<string, number>`,
+    `enum MyEnum { foo, bar, baz }
+     type MyDict = SingleKeyDictionary<MyEnum, object>`,
+  ],
+  invalid: [
+    {
+      code:
+        `type MyKey = string | boolean
+         type MyDict = SingleKeyDictionary<MyKey, any>`,
+      errors: [{ messageId: 'stringKey' }]
+    },
+    {
+      code: `type MyDict = SingleKeyDictionary<string | number, any>`,
+      errors: [{ messageId: 'stringKey' }]
+    },
+    {
+      code: `type MyDict = SingleKeyDictionary<boolean, any>`,
+      errors: [{ messageId: 'stringKey' }]
+    },
+    {
+      code: `type MyDict = SingleKeyDictionary<object, any>`,
+      errors: [{ messageId: 'stringKey' }]
+    }
+  ],
+})