from unittest import TestCase
class AreaStrategy:
    def calculate(self, x, y):
        if x > 0 and y > 0: return x * y
        if x < 0 or y < 0: raise ValueError('dfsdf')
        else: return 0

class TestAreaStrategy(TestCase):
    def setUp(self):
        self._width = 90
        self._height = 144
        self._strategy = AreaStrategy()
    def testCalculate(self):
        strat = self._strategy
        self.assertEqual(self._width * self._height, strat.calculate(self._width, self._height))
        self.assertEqual(0, strat.calculate(self._width, 0))
        self.assertRaises(ValueError, strat.calculate, -self._width, self._height)
        self.assertRaises(ValueError, strat.calculate, -self._width, 0)

if __name__ == '__main__':
    import unittest
    unittest.main()

Ran 1 test in 0.001s
OK
Traceback (most recent call last):
    unittest.main()
  File "C:\Python33\lib\unittest\main.py", line 125, in __init__
    self.runTests()
  File "C:\Python33\lib\unittest\main.py", line 263, in runTests
    sys.exit(not self.result.wasSuccessful())
SystemExit: False