Add the unittest import for test_fake_quant.py (pytorch#28815)

Summary:
Pull Request resolved: pytorch#28815

Add the unittest import
ghstack-source-id: 92789329

Test Plan: CI

Differential Revision: D18191989

fbshipit-source-id: c54e0309e21156c33e4fec01bfba17a1c30463c9

test/test_fake_quant.py

@@ -10,12 +10,13 @@
 from torch.quantization import FakeQuantize
 from torch.quantization import default_observer, default_per_channel_weight_observer
 import io
+import unittest
+
 # Reference method for fake quantize
 def _fake_quantize_per_tensor_affine_reference(X, scale, zero_point, quant_min, quant_max):
     res = (torch.clamp(torch.round(X.cpu() * (1.0 / scale) + zero_point), quant_min, quant_max) - zero_point) * scale
     return res
 
-
 # Reference method for the gradient of the fake quantize operator
 def _fake_quantize_per_tensor_affine_grad_reference(dY, X, scale, zero_point, quant_min, quant_max):
     Xq = torch.round(X.cpu() * (1.0 / scale) + zero_point)