add failing test for postcss config

tests/fixtures/no-unknown-class/postcss-config/Component.jsx

@@ -0,0 +1,3 @@
+export default function Component() {
+  return <div className="my-custom-component"></div>;
+}

tests/fixtures/no-unknown-class/postcss-config/components.css

@@ -0,0 +1,5 @@
+@layer components {
+  .my-custom-component {
+    @apply bg-green-100 text-black;
+  }
+}

tests/fixtures/no-unknown-class/postcss-config/postcss.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  plugins: ["postcss-import", "postcss-nested", "tailwindcss", "postcss-extend"],
+};

tests/fixtures/no-unknown-class/postcss-config/styles.css

@@ -0,0 +1,5 @@
+@import "./components.css";
+
+@tailwind base;
+@tailwind utilities;
+@tailwind components;

tests/fixtures/no-unknown-class/postcss-config/tailwind.config.js

@@ -0,0 +1,12 @@
+module.exports = {
+  future: {
+    // removeDeprecatedGapUtilities: true,
+    // purgeLayersByDefault: true,
+  },
+  purge: [],
+  theme: {
+    extend: {},
+  },
+  variants: {},
+  plugins: [],
+};

tests/lib/rules/no-unknown-class.test.ts

@@ -1,3 +1,6 @@
+import fs from "fs";
+import path from "path";
+
 import { RuleTester } from "eslint";
 
 import loadTestCases from "../../load-test-cases";
@@ -12,4 +15,20 @@ const tester = new RuleTester({
   },
 });
 
-tester.run("no-unknown-class", rule, loadTestCases("no-unknown-class"));
+function postcssConfigTestCase(): RuleTester.ValidTestCase {
+  const fixtureRoot = path.join(__dirname, "../../fixtures/no-unknown-class/postcss-config");
+
+  function read(filename: string): string {
+    return fs.readFileSync(path.join(fixtureRoot, filename), { encoding: "utf-8" });
+  }
+
+  return {
+    filename: "postcss-config",
+    code: read("Component.jsx"),
+    options: [{ config: { postcss: true }, stylesheet: path.join(fixtureRoot, "styles.css") }],
+  };
+}
+
+const cases = loadTestCases("no-unknown-class");
+cases.valid.push(postcssConfigTestCase());
+tester.run("no-unknown-class", rule, cases);