Add basic verify_grad test to check transformer's grad wrt to inputs

theano/gpuarray/tests/test_dnn.py

@@ -2480,7 +2480,7 @@ def test_dnn_spatialtf_grad():
     utt.seed_rng()
 
     # Generate random set of RGB images with 256x256 resolution (pixel values in [0, 255])
-    img_dims = (10, 256, 256, 3)  # images are usually NHWC
+    img_dims = (1, 256, 256, 3)  # images are usually NHWC
     img = np.random.randint(low=0, high=256, size=img_dims)
     # Convert from NHWC to NCHW
     img = np.transpose(img, axes=(0, 3, 1, 2)).astype(theano.config.floatX)
@@ -2510,3 +2510,5 @@ def test_dnn_spatialtf_grad():
 
     assert any([isinstance(node.op, dnn.GpuDnnTransformerGradT)
                 for node in grad_fn.maker.fgraph.toposort()])
+
+    utt.verify_grad(dnn.dnn_spatialtf(t_img, theta), [img], mode=mode_with_gpu)
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