Improved the test for non_clusterable_layer that demonstrates that

the layer can be clusterable if weights are not allocated.

Change-Id: If26bf41355c380dc564aff5e2309dc502abe91f2

Author: wwwind

tensorflow_model_optimization/python/core/clustering/keras/cluster_test.py

@@ -170,7 +170,10 @@ def testClusterCustomNonClusterableLayer(self):
     an exception.
     """
     custom_non_clusterable_layer = self.custom_non_clusterable_layer
-    # We need to build weights before check.
+    # Once layer is empty with no weights allocated, clustering is supported.
+    cluster_wrapper.ClusterWeights(custom_non_clusterable_layer,
+                                  **self.params)
+    # We need to build weights before check that clustering is not supported.
     custom_non_clusterable_layer.build(input_shape=(10, 10))
     with self.assertRaises(ValueError):
       cluster_wrapper.ClusterWeights(custom_non_clusterable_layer,