Refactor speechcommands unittest (#1136)

test/torchaudio_unittest/datasets/speechcommands_test.py

 import os
 from pathlib import Path
 
-from torchaudio.datasets import speechcommands
-
 from torchaudio_unittest.common_utils import (
     TempDirMixin,
     TorchaudioTestCase,
@@ -11,7 +9,9 @@ from torchaudio_unittest.common_utils import (
     save_wav,
 )
 
-LABELS = [
+from torchaudio.datasets import speechcommands
+
+_LABELS = [
     "bed",
     "bird",
     "cat",
@@ -49,28 +49,21 @@ LABELS = [
 ]
 
 
-class TestSpeechCommands(TempDirMixin, TorchaudioTestCase):
-    backend = "default"
-
-    root_dir = None
-    samples = []
-    train_samples = []
-    valid_samples = []
-    test_samples = []
-
-    @classmethod
-    def setUpClass(cls):
-        cls.root_dir = cls.get_base_temp_dir()
-        dataset_dir = os.path.join(
-            cls.root_dir, speechcommands.FOLDER_IN_ARCHIVE, speechcommands.URL
-        )
+def get_mock_dataset(dataset_dir):
+    """
+    dataset_dir: directory to the mocked dataset
+    """
+    mocked_samples = []
+    mocked_train_samples = []
+    mocked_valid_samples = []
+    mocked_test_samples = []
     os.makedirs(dataset_dir, exist_ok=True)
     sample_rate = 16000  # 16kHz sample rate
     seed = 0
     valid_file = os.path.join(dataset_dir, "validation_list.txt")
     test_file = os.path.join(dataset_dir, "testing_list.txt")
     with open(valid_file, "w") as valid, open(test_file, "w") as test:
-            for label in LABELS:
+        for label in _LABELS:
             path = os.path.join(dataset_dir, label)
             os.makedirs(path, exist_ok=True)
             for j in range(6):
@@ -96,15 +89,34 @@ class TestSpeechCommands(TempDirMixin, TorchaudioTestCase):
                         speaker,
                         utterance,
                     )
-                        cls.samples.append(sample)
+                    mocked_samples.append(sample)
                     if j < 2:
-                            cls.train_samples.append(sample)
+                        mocked_train_samples.append(sample)
                     elif j < 4:
                         valid.write(f'{label}/{filename}\n')
-                            cls.valid_samples.append(sample)
+                        mocked_valid_samples.append(sample)
                     elif j < 6:
                         test.write(f'{label}/{filename}\n')
-                            cls.test_samples.append(sample)
+                        mocked_test_samples.append(sample)
+    return mocked_samples, mocked_train_samples, mocked_valid_samples, mocked_test_samples
+
+
+class TestSpeechCommands(TempDirMixin, TorchaudioTestCase):
+    backend = "default"
+
+    root_dir = None
+    samples = []
+    train_samples = []
+    valid_samples = []
+    test_samples = []
+
+    @classmethod
+    def setUpClass(cls):
+        cls.root_dir = cls.get_base_temp_dir()
+        dataset_dir = os.path.join(
+            cls.root_dir, speechcommands.FOLDER_IN_ARCHIVE, speechcommands.URL
+        )
+        cls.samples, cls.train_samples, cls.valid_samples, cls.test_samples = get_mock_dataset(dataset_dir)
 
     def _testSpeechCommands(self, dataset, data_samples):
         num_samples = 0