Added explaination for a test following code review.

theano/tensor/tests/test_blas.py

@@ -768,6 +768,13 @@ def test_gemm_opt_vector_stuff():
 
 
 def test_gemm_unrolled():
+    """This test that the gemm optimizer remove the dot22 that was
+    present in the graph. Otherwise, this add a gemm, but still
+    compute the dot22.
+
+    This was not always the case in the with this the following code.
+
+    """
     batch_size = 100
     rep_size = 40
     rng = numpy.random.RandomState([1, 2, 3])
@@ -799,7 +806,8 @@ def test_gemm_unrolled():
                       if isinstance(node.op, (theano.tensor.Dot,
                                               theano.tensor.blas.Dot22,
                                               theano.tensor.blas.Gemm))])
-
+        # Each num_rounds add 3 dot, but one of them is always the same.
+        # So the final graph should have 1 + 2* num_rounds dot varient op.
         assert nb_dot == num_rounds * 2 + 1, nb_dot
 
         unrolled_theano()