new_contents: import unittest
  from singleNumber import Solution
  
  class TestSingleNumber(unittest.TestCase):
      def setUp(self):
          self.solution = Solution()
  
      def testArrayOfSingleIntReturnsOnlyValue(self):
          A = [1]
          self.assertEqual(self.solution.singleNumber(A), 1)
  
      def testArrayOfTwoTypesOfNumbersReturnsOnlySingleValueNumber(self):
          A = [2, 2, 1]
          self.assertEqual(self.solution.singleNumber(A), 1)
  
      def testArrayOfThreeTypesOfNumbersReturnsOnlySingleValueNumber(self):
          A = [2, 3, 1, 3, 2]
          self.assertEqual(self.solution.singleNumber(A), 1)
  
  if __name__ == '__main__':
      unittest.main()
  
subject: Add 3 test cases for singleNumber problem.