Add buffer test

lib/functions.php

@@ -43,7 +43,6 @@ function pipe(InputStream $source, OutputStream $destination): Promise {
 
 /**
  * @param \Amp\ByteStream\InputStream  $source
- * @param \Amp\ByteStream\OutputStream $destination
  *
  * @return \Amp\Promise
  */

test/BufferTest.php

@@ -0,0 +1,20 @@
+<?php
+
+
+namespace Amp\ByteStream\Test;
+
+use function Amp\ByteStream\buffer;
+use Amp\ByteStream\IteratorStream;
+use Amp\Iterator;
+use Amp\PHPUnit\TestCase;
+use function Amp\Promise\wait;
+
+class BufferTest extends TestCase
+{
+    public function testBuffer()
+    {
+        $stream = new IteratorStream(Iterator\fromIterable(["abc", "def", "g"], 10));
+
+        $this->assertSame("abcdefg", wait(buffer($stream)));
+    }
+}