releasetools: Add a common base class for unittests.

All the releasetools unittests extend the common base class of
test_utils.ReleaseToolsTestCase. Define tearDown() in the base class to
do the clean-up works.

Test: `pylint --rcfile=pylintrc test_*.py`
Test: `python -m unittest discover .`
Change-Id: I51775d964ef032dcdf3bb89c55e1a31371cde708

tools/releasetools/test_common.py

@@ -19,7 +19,6 @@ import os
 import subprocess
 import tempfile
 import time
-import unittest
 import zipfile
 from hashlib import sha1
 
@@ -44,7 +43,8 @@ def get_2gb_string():
     yield '\0' * (step_size - block_size)
 
 
-class CommonZipTest(unittest.TestCase):
+class CommonZipTest(test_utils.ReleaseToolsTestCase):
+
   def _verify(self, zip_file, zip_file_name, arcname, expected_hash,
               test_file_name=None, expected_stat=None, expected_mode=0o644,
               expected_compress_type=zipfile.ZIP_STORED):
@@ -359,7 +359,7 @@ class CommonZipTest(unittest.TestCase):
       os.remove(zip_file.name)
 
 
-class CommonApkUtilsTest(unittest.TestCase):
+class CommonApkUtilsTest(test_utils.ReleaseToolsTestCase):
   """Tests the APK utils related functions."""
 
   APKCERTS_TXT1 = (
@@ -407,9 +407,6 @@ class CommonApkUtilsTest(unittest.TestCase):
   def setUp(self):
     self.testdata_dir = test_utils.get_testdata_dir()
 
-  def tearDown(self):
-    common.Cleanup()
-
   @staticmethod
   def _write_apkcerts_txt(apkcerts_txt, additional=None):
     if additional is None:
@@ -523,14 +520,11 @@ class CommonApkUtilsTest(unittest.TestCase):
         {})
 
 
-class CommonUtilsTest(unittest.TestCase):
+class CommonUtilsTest(test_utils.ReleaseToolsTestCase):
 
   def setUp(self):
     self.testdata_dir = test_utils.get_testdata_dir()
 
-  def tearDown(self):
-    common.Cleanup()
-
   def test_GetSparseImage_emptyBlockMapFile(self):
     target_files = common.MakeTempFile(prefix='target_files-', suffix='.zip')
     with zipfile.ZipFile(target_files, 'w') as target_files_zip:
@@ -935,7 +929,7 @@ class CommonUtilsTest(unittest.TestCase):
           AssertionError, common.LoadInfoDict, target_files_zip, True)
 
 
-class InstallRecoveryScriptFormatTest(unittest.TestCase):
+class InstallRecoveryScriptFormatTest(test_utils.ReleaseToolsTestCase):
   """Checks the format of install-recovery.sh.
 
   Its format should match between common.py and validate_target_files.py.
@@ -994,6 +988,3 @@ class InstallRecoveryScriptFormatTest(unittest.TestCase):
                              recovery_image, boot_image, self._info)
     validate_target_files.ValidateInstallRecoveryScript(self._tempdir,
                                                         self._info)
-
-  def tearDown(self):
-    common.Cleanup()