test: add test for stream unpipe with 'data' listeners

PR-URL: nodejs#18516
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-stream-pipe-flow-after-unpipe.js

@@ -0,0 +1,29 @@
+'use strict';
+const common = require('../common');
+const { Readable, Writable } = require('stream');
+
+// Tests that calling .unpipe() un-blocks a stream that is paused because
+// it is waiting on the writable side to finish a write().
+
+const rs = new Readable({
+  highWaterMark: 1,
+  // That this gets called at least 20 times is the real test here.
+  read: common.mustCallAtLeast(() => rs.push('foo'), 20)
+});
+
+const ws = new Writable({
+  highWaterMark: 1,
+  write: common.mustCall(() => {
+    // Ignore the callback, this write() simply never finishes.
+    setImmediate(() => rs.unpipe(ws));
+  })
+});
+
+let chunks = 0;
+rs.on('data', common.mustCallAtLeast(() => {
+  chunks++;
+  if (chunks >= 20)
+    rs.pause();  // Finish this test.
+}));
+
+rs.pipe(ws);