Fix transducer test skip logic (#1253)

test/torchaudio_unittest/transducer_test.py

+import unittest
 import torch
 from torchaudio.prototype.transducer import RNNTLoss
 
-from torchaudio_unittest import common_utils
+from torchaudio_unittest.common_utils import TorchaudioTestCase
 
 
 def get_data_basic(device):
@@ -241,6 +242,14 @@ def compute_with_pytorch_transducer(data):
     return costs, gradients
 
 
+def skipIfNoTransducer(test_item):
+    try:
+        torch.ops.torchaudio.rnnt_loss
+        return test_item
+    except RuntimeError:
+        return unittest.skip("torchaudio C++ extension is not compiled with RNN transducer loss")(test_item)
+
+
 class TransducerTester:
     def test_basic_fp16_error(self):
         rnnt_loss = RNNTLoss()
@@ -271,6 +280,6 @@ class TransducerTester:
         self.assertEqual(gradients, ref_gradients, atol=atol, rtol=rtol)
 
 
-@common_utils.skipIfNoExtension
-class CPUTransducerTester(TransducerTester, common_utils.PytorchTestCase):
+@skipIfNoTransducer
+class CPUTransducerTester(TransducerTester, TorchaudioTestCase):
     device = "cpu"