stream: add final method

Adds the ability to for write streams to have an _final method which acts
similarly to the _flush method that transform streams have but is called before
the finish event is emitted and if asynchronous delays the stream from
finishing.  The `final` option may also be passed in order to set it.

PR-URL: https://github.com/nodejs/node/pull/12828
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>

1 files changed, 12 insertions, 12 deletions

diff --git a/test/parallel/test-stream-transform-constructor-set-methods.js b/test/parallel/test-stream-transform-constructor-set-methods.js
index 1423f4de10..3e1325c0fd 100644
--- a/test/parallel/test-stream-transform-constructor-set-methods.js
+++ b/test/parallel/test-stream-transform-constructor-set-methods.js
@@ -1,24 +1,25 @@
 'use strict';
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 
 const Transform = require('stream').Transform;
 
-let _transformCalled = false;
-function _transform(d, e, n) {
-  _transformCalled = true;
+const _transform = common.mustCall(function _transform(d, e, n) {
   n();
-}
+});
 
-let _flushCalled = false;
-function _flush(n) {
-  _flushCalled = true;
+const _final = common.mustCall(function _final(n) {
   n();
-}
+});
+
+const _flush = common.mustCall(function _flush(n) {
+  n();
+});
 
 const t = new Transform({
   transform: _transform,
-  flush: _flush
+  flush: _flush,
+  final: _final
 });
 
 const t2 = new Transform({});
@@ -34,6 +35,5 @@ assert.throws(() => {
 process.on('exit', () => {
   assert.strictEqual(t._transform, _transform);
   assert.strictEqual(t._flush, _flush);
-  assert.strictEqual(_transformCalled, true);
-  assert.strictEqual(_flushCalled, true);
+  assert.strictEqual(t._final, _final);
 });