Add Autograd test for T.Resample (#1416)

test/torchaudio_unittest/transforms/autograd_test_impl.py

@@ -71,3 +71,9 @@ class AutogradTestMixin(TestBaseMixin):
         transform = T.MFCC(sample_rate=sample_rate, log_mels=log_mels)
         waveform = get_whitenoise(sample_rate=sample_rate, duration=0.05, n_channels=2)
         self.assert_grad(transform, [waveform])
+
+    @parameterized.expand([(8000, 8000), (8000, 4000), (4000, 8000)])
+    def test_resample(self, orig_freq, new_freq):
+        transform = T.Resample(orig_freq=orig_freq, new_freq=new_freq)
+        waveform = get_whitenoise(sample_rate=8000, duration=0.05, n_channels=2)
+        self.assert_grad(transform, [waveform])