test: add test of stream Transform

Add a test case of Transform constructor without new.

PR-URL: https://github.com/nodejs/node/pull/17303
Reviewed-By: Ron Korving <ron@ronkorving.nl>
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

test/parallel/test-stream2-transform.js

@@ -96,6 +96,13 @@ const Transform = require('_stream_transform');
   assert(pt instanceof PassThrough);
 }
 
+{
+  // Verify transform constructor behavior
+  const pt = Transform();
+
+  assert(pt instanceof Transform);
+}
+
 {
   // Perform a simple transform
   const pt = new Transform();