golang: Test that buffered channel releases objects from buffer on chan GC

Currently it behaves correctly, but this aspect will need to be
explicitly cared about when channel implementation moves to C. Add test
to make sure it won't regress.

golang/golang_test.py

@@ -26,6 +26,7 @@ from pytest import raises
 from os.path import dirname
 import os, sys, threading, inspect, subprocess
 from six.moves import range as xrange
+import gc, weakref
 
 import golang
 from golang import _chan_recv, _chan_send
@@ -183,6 +184,23 @@ def test_chan():
     ch.close()
     assert done.recv() == 'b'
 
+    # buffered: releases objects in buffer on chan gc
+    ch = chan(3)
+    class Obj(object): pass
+    obj1 = Obj(); w1 = weakref.ref(obj1); assert w1() is obj1
+    obj2 = Obj(); w2 = weakref.ref(obj2); assert w2() is obj2
+    ch.send(obj1)
+    ch.send(obj2)
+    del obj1
+    del obj2
+    gc.collect()
+    assert w1() is not None
+    assert w2() is not None
+    ch = None
+    gc.collect()
+    assert w1() is None
+    assert w2() is None
+
 
 # benchmark sync chan send/recv.
 def bench_chan(b):