test the fix for the merge optimization

theano/scan_module/tests/test_scan.py

@@ -3463,6 +3463,27 @@ class T_Scan(unittest.TestCase):
         )
         tensor.grad(out[-1], w)
 
+    def test_scan_merge_nodes(self):
+        inps = tensor.vector()
+        state = tensor.scalar()
+        y1, _ = theano.scan(lambda x,y: x*y,
+                            sequences = inps,
+                            outputs_info = state,
+                            n_steps = 5)
+
+        y2, _ = theano.scan(lambda x,y : (x+y, theano.scan_module.until(x>0)),
+                            sequences = inps,
+                            outputs_info = state,
+                            n_steps = 5)
+        scan_node1 = y1.owner.inputs[0].owner
+        assert isinstance(scan_node1.op, theano.scan_module.scan_op.Scan)
+        scan_node2 = y2.owner.inputs[0].owner
+        assert isinstance(scan_node2.op, theano.scan_module.scan_op.Scan)
+        opt_obj = theano.scan_module.scan_opt.ScanMerge()
+        # Test the method belongs_to of this class. Specifically see if it
+        # detects the two scan_nodes as not being similar
+        assert not opt_obj.belongs_to_set(scan_node1, [scan_node2])
+        assert not opt_obj.belongs_to_set(scan_node2, [scan_node1])
 
 
 def test_speed():