test: test streambase already has a consumer

Author: MrJithil

test/parallel/test-whatwg-webstreams-adapters-streambase.js

@@ -65,3 +65,12 @@ const {
   const readable = newReadableStreamFromStreamBase(stream);
   readable.cancel().then(common.mustCall());
 }
+
+{
+  const stream = new JSStream();
+  stream.onread = () => {};
+  assert.throws(() => newReadableStreamFromStreamBase(stream), {
+    code: 'ERR_INVALID_STATE',
+    message: /StreamBase already has a consumer/
+  });
+}