@unittest.skipIf(not os.path.exists('/usr/bin/diff'),
                   'requires /usr/bin/diff')
  def test_Diff_SameData_ExternalDiff(self):
    os.environ['TEST_DIFF'] = '/usr/bin/diff'
    basetest._WriteTestData('b\n', self.data1_file)
    basetest._WriteTestData('b\n', self.data2_file)
    # This must not raise an exception:
    basetest._Diff(self.data1_file, self.data2_file)
Test the internal _Diff method when TEST_DIFF is in the env.
dataset/ETHPy150Open google/google-apputils/tests/basetest_test.py/GoogleTestBaseUnitTest.test_Diff_SameData_ExternalDiff