test: add regression test for unpipe()

Since 2e568d9 there is a bug where unpiping a stream from a readable stream that has `_readableState.pipesCount > 1` will cause it to remove the first stream in the `_.readableState.pipes` array no matter where in the list the `dest` stream was. Ref: #9553 PR-URL: #9171 Reviewed-By: Evan Lucas <evanlucas@me.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Luigi Pinca <luigipinca@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Myles Borins <myles.borins@gmail.com>
nodejs · MylesBorins · Sep 30, 2016 · Oct 18, 2016 · Oct 18, 2016 · Oct 12, 2016
commit a1d7201df3f4825df4c36bb8b948a508f0869015
diff --git a/test/parallel/test-stream-pipe-unpipe-streams.js b/test/parallel/test-stream-pipe-unpipe-streams.js
@@ -0,0 +1,32 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+const Stream = require('stream');
+const Readable = Stream.Readable;
+const Writable = Stream.Writable;
+
+const source = Readable({read: () => {}});
+const dest1 = Writable({write: () => {}});
+const dest2 = Writable({write: () => {}});
+
+source.pipe(dest1);
+source.pipe(dest2);
+
+dest1.on('unpipe', common.mustCall(() => {}));
+dest2.on('unpipe', common.mustCall(() => {}));
+
+assert.strictEqual(source._readableState.pipes[0], dest1);
+assert.strictEqual(source._readableState.pipes[1], dest2);
+assert.strictEqual(source._readableState.pipes.length, 2);
+
+// Should be able to unpipe them in the reverse order that they were piped.
+
+source.unpipe(dest2);
+
+assert.strictEqual(source._readableState.pipes, dest1);
+assert.notStrictEqual(source._readableState.pipes, dest2);
+
+source.unpipe(dest1);
+
+assert.strictEqual(source._readableState.pipes, null);