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Python 3: An interactive deep dive

More Halting, More Fire

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Along with testing numbers that are too large, you need to test numbers that are too small. As we noted in our functional requirements, Roman numerals cannot express 0 or negative numbers.

Python 3.5
import roman2
print (roman2.to_roman(0))
#''
print (roman2.to_roman(-1))
#''

Well that’s not good. Let’s add tests for each of these conditions.

Python 3.5
import unittest
class ToRomanBadInput(unittest.TestCase):
    def test_too_large(self):
        '''to_roman should fail with large input'''
        self.assertRaises(roman3.OutOfRangeError, roman3.to_roman, 4000)  #①
    def test_zero(self):
        '''to_roman should fail with 0 input'''
        self.assertRaises(roman3.OutOfRangeError, roman3.to_roman, 0)     #②
    def test_negative(self):
        '''to_roman should fail with negative input'''
        self.assertRaises(roman3.OutOfRangeError, roman3.to_roman, -1)    #③

① The test_too_large() ...