diff --git a/packages/language-services/src/features/__tests__/do-diagnostics.test.ts b/packages/language-services/src/features/__tests__/do-diagnostics.test.ts
new file mode 100644
index 00000000..128597b7
--- /dev/null
+++ b/packages/language-services/src/features/__tests__/do-diagnostics.test.ts
@@ -0,0 +1,65 @@
+import { test, assert, beforeEach } from "vitest";
+import {
+	defaultConfiguration,
+	getLanguageService,
+} from "../../language-services";
+import { DiagnosticSeverity } from "../../language-services-types";
+import { getOptions } from "../../utils/test-helpers";
+
+const { fileSystemProvider, ...rest } = getOptions();
+const ls = getLanguageService({ fileSystemProvider, ...rest });
+
+beforeEach(() => {
+	ls.clearCache();
+	ls.configure(defaultConfiguration);
+});
+
+test("reports an unknown at-rule", async () => {
+	const document = fileSystemProvider.createDocument(`
+@tailwind base;
+`);
+
+	const result = await ls.doDiagnostics(document);
+
+	assert.deepStrictEqual(result, [
+		{
+			code: "unknownAtRules",
+			message: "Unknown at rule @tailwind",
+			range: {
+				start: {
+					line: 1,
+					character: 0,
+				},
+				end: {
+					line: 1,
+					character: 9,
+				},
+			},
+			severity: DiagnosticSeverity.Warning,
+			source: "scss",
+		},
+	]);
+});
+
+test("ignores unknown at-rules if configured", async () => {
+	const document = fileSystemProvider.createDocument(`
+@tailwind base;
+`);
+
+	ls.configure({
+		...defaultConfiguration,
+		scss: {
+			...defaultConfiguration.scss,
+			diagnostics: {
+				...defaultConfiguration.scss.diagnostics,
+				lint: {
+					...defaultConfiguration.scss.diagnostics.lint,
+					unknownAtRules: "ignore",
+				},
+			},
+		},
+	});
+	const result = await ls.doDiagnostics(document);
+
+	assert.deepStrictEqual(result, []);
+});