test(rollup): validate preserved import dedupe

Author: wjhsf

packages/@lwc/rollup-plugin/src/__tests__/importDedupe/fixtures/basic/basic.js

@@ -0,0 +1,7 @@
+import { LightningElement } from 'lwc';
+import { renderer as a } from 'lwc';
+import { renderer as b } from 'lwc';
+
+export default class extends LightningElement {
+    prop = [a, b];
+}

packages/@lwc/rollup-plugin/src/__tests__/importDedupe/importDedupe.spec.ts

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2022, salesforce.com, inc.
+ * All rights reserved.
+ * SPDX-License-Identifier: MIT
+ * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+ */
+import path from 'node:path';
+import { it, expect } from 'vitest';
+import { rollup } from 'rollup';
+
+import lwc from '../../index';
+import type { RollupLwcOptions } from '../../index';
+import type { RollupLog } from 'rollup';
+
+async function runRollup(
+    pathname: string,
+    options: RollupLwcOptions
+): Promise<{ code: string; warnings: RollupLog[] }> {
+    const warnings: RollupLog[] = [];
+    const bundle = await rollup({
+        input: path.resolve(import.meta.dirname, pathname),
+        plugins: [lwc(options)],
+        external: ['lwc'],
+        onwarn(warning) {
+            warnings.push(warning);
+        },
+    });
+
+    const { output } = await bundle.generate({
+        format: 'esm',
+    });
+
+    return {
+        code: output[0].code,
+        warnings,
+    };
+}
+
+// This test validates the behavior of rollup because import deduping was handled by
+// @lwc/babel-plugin-component prior to v9 and we want to ensure there are no regressions
+it('merges duplicate imports', async () => {
+    const { code, warnings } = await runRollup('fixtures/basic/basic.js', {});
+    const lwcImport = /import \{ ([^}]+?) \} from 'lwc'/g;
+    const imports = Array.from(code.matchAll(lwcImport));
+    expect(warnings).toHaveLength(0);
+    expect(imports).toHaveLength(1);
+    const specifiers = imports[0][1];
+    expect(specifiers).toContain('renderer');
+    expect(specifiers).not.toContain('renderer as');
+});