Add tests

packages/unified-lint-rule/package.json

@@ -40,7 +40,8 @@
     "vfile": "^5.0.0"
   },
   "scripts": {
-    "build": "rimraf \"lib/**/*.d.ts\" && tsc && type-coverage"
+    "build": "rimraf \"lib/**/*.d.ts\" && tsc && type-coverage",
+    "test": "tape test.js"
   },
   "xo": false,
   "typeCoverage": {

packages/unified-lint-rule/test.js

@@ -0,0 +1,35 @@
+import test from 'tape'
+import {VFile} from 'vfile'
+import {lintRule} from './index.js'
+
+test('`this` value', async (t) => {
+  t.plan(1)
+  const processor = {}
+  lintRule('this-value', rule).call(processor)(
+    undefined /* tree */,
+    new VFile(),
+    () => {} /* next */
+  )
+
+  function rule() {
+    t.equal(
+      this,
+      processor,
+      "rule's `this` value should be the processor using it"
+    )
+  }
+})
+
+test('`fileSet` argument', async (t) => {
+  t.plan(1)
+  const expected = {}
+  lintRule('fileSet-argument', rule)(undefined /* options */, expected)(
+    undefined /* tree */,
+    new VFile(),
+    () => {} /* next */
+  )
+
+  function rule(tree, file, options, actual) {
+    t.equal(actual, expected, 'should pass the `fileSet` argument to the rule')
+  }
+})