From 5995a50f29027bc4f235253f227f299d68d5c428 Mon Sep 17 00:00:00 2001
From: Ardis Lu <ardisglu@gmail.com>
Date: Mon, 28 Jul 2025 23:35:40 -0700
Subject: [PATCH] Add tests for `instanceof` behavior

In preparation for possible future refactoring for these classes to return a `Proxy` object (this pattern is required to simulate dynamic superclasses, e.g., `CSVReader` returning either `ReadableStream` OR `TransformStream` depending on constructor argument). If such refactoring takes place, these tests will check that `Proxy` was implemented correctly and maintain backwards compatibility.
---
 test/core.test.js          | 17 +++++++++++++++++
 test/normalization.test.js |  8 ++++++++
 2 files changed, 25 insertions(+)

diff --git a/test/core.test.js b/test/core.test.js
index 4445bcf..7cde8e5 100644
--- a/test/core.test.js
+++ b/test/core.test.js
@@ -293,6 +293,12 @@ suite('CSVReader', { concurrency: true }, () => {
     const c = await s.getReader().read().then(({ value }) => value);
     deepStrictEqual(c, undefined);
   });
+  test('works with instanceof', { concurrency: true }, async () => {
+    const path = new URL('./data/simple.csv', import.meta.url);
+    const s = new CSVReader(path);
+    deepStrictEqual(s instanceof CSVReader, true);
+    await s.cancel();
+  });
 });
 
 suite('CSVTransformer', { concurrency: true }, () => {
@@ -547,6 +553,10 @@ suite('CSVTransformer', { concurrency: true }, () => {
       ]));
     deepStrictEqual(fn.mock.callCount(), 2);
   });
+  test('works with instanceof', { concurrency: true }, async () => {
+    const s = new CSVTransformer(r => r);
+    deepStrictEqual(s instanceof CSVTransformer, true);
+  });
 });
 
 suite('CSVWriter', { concurrency: true }, () => {
@@ -708,6 +718,13 @@ suite('CSVWriter', { concurrency: true }, () => {
     await rejects(writer.write('b'));
     await new CSVReader(temp).pipeTo(csvStreamEqualWritable([['a']]));
   });
+  test('works with instanceof', { concurrency: true }, async (t) => {
+    const temp = await createTempFile();
+    t.after(async () => await unlink(temp));
+    const s = new CSVWriter(temp);
+    deepStrictEqual(s instanceof CSVWriter, true);
+    await s.abort();
+  });
 });
 
 suite('CSVWriter status', { concurrency: true }, () => {
diff --git a/test/normalization.test.js b/test/normalization.test.js
index 620b4cf..bef63dd 100644
--- a/test/normalization.test.js
+++ b/test/normalization.test.js
@@ -461,6 +461,10 @@ suite('CSVNormalizer', { concurrency: true }, () => {
         ['a', 'b']
       ]));
   });
+  test('works with instanceof', { concurrency: true }, async () => {
+    const s = new CSVNormalizer([]);
+    deepStrictEqual(s instanceof CSVNormalizer, true);
+  });
 });
 
 suite('CSVDenormalizer', { concurrency: true }, () => {
@@ -488,6 +492,10 @@ suite('CSVDenormalizer', { concurrency: true }, () => {
         ['a2', 'b2']
       ]));
   });
+  test('works with instanceof', { concurrency: true }, async () => {
+    const s = new CSVDenormalizer();
+    deepStrictEqual(s instanceof CSVDenormalizer, true);
+  });
 });
 
 suite('CSVNormalizer and CSVDenormalizer end-to-end', { concurrency: true }, () => {
-- 
2.47.3