Test for #3363

test/IdAttributePluginTest.js

@@ -0,0 +1,19 @@
+import test from "ava";
+
+import { IdAttributePlugin } from "../src/Plugins/IdAttributePlugin.js";
+import Eleventy from "../src/Eleventy.js";
+
+test("Using the transform (and the filter too)", async (t) => {
+  let elev = new Eleventy("./test/stubs-virtual/", "./test/stubs-virtual/_site", {
+    config: function (eleventyConfig) {
+      eleventyConfig.addPlugin(IdAttributePlugin);
+
+      eleventyConfig.addTemplate("test.njk", `<h1>This is a heading</h1><h2 id="already">This is another heading</h2>`, {});
+    },
+  });
+
+  elev.disableLogger();
+
+  let results = await elev.toJSON();
+	t.is(results[0].content, `<h1 id="this-is-a-heading">This is a heading</h1><h2 id="already">This is another heading</h2>`);
+});