20.9. Exercises

1. A function named reverse takes a string argument, reverses it, and returns the result:

   def reverse(astring):
       """Returns the reverse of `astring`"""
   

   Complete the assert statements in the ActiveCode editor below to create a unit test for reverse. Your asserts should check that reverse works properly for the following test cases (“Input” refers to the value passed as a parameter, and “Expected Output” is the result returned from reverse):

                Input    Expected Output
                -------- ---------------
   Test Case 1: 'abc'    'cba'
   Test Case 2: 'b'      'b'
   Test Case 3: ''       ''
   

   def test_reverse(): # Complete the assert statements below assert ________________ assert ________________ assert ________________ ==== from unittest.gui import TestCaseGui testABC = False testB = False testEmpty = False def reverse(astring): """Returns the reverse of `astring`""" global testABC, testB, testEmpty if astring == 'abc': testABC = True elif astring == 'b': testB = True elif astring == '': testEmpty = True l = list(astring) l.reverse() return ''.join(l) class myTests(TestCaseGui): def testOne(self): test_reverse() code = self.getEditorText().replace(' ','').replace('"', '').replace("'", '') self.assertTrue(testABC and '==cba' in code, "Assert tested 'abc'") self.assertTrue(testB and '==b' in code, "Assert tested 'b'") self.assertTrue(testEmpty and '==\n' in code, "Assert tested ''") myTests().main()

   If you’re not sure how to get started with this one, review Writing Unit Tests.

   assert reverse('abc') == 'cba'
   assert reverse('b') == 'b'
   assert reverse('') == ''
   

2. A function named stripletters takes a string argument, removes all letters from it, and displays the result (see below). However, this function is not testable.

   Modify the function so that it can be tested with the assert statements that follow.

   def stripletters(msg): result = '' for ch in msg: if not ch.isalpha(): result += ch print(result) assert stripletters('ab12c') == '12' assert stripletters('12') == '12' ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(stripletters('ab12c'), '12', "stripletters('ab12c') == '12'") self.assertEqual(stripletters('12'), '12', "stripletters('12') == '12'") myTests().main()

   Review Designing Testable Functions.

   def stripletters(msg):
       result = ''
       for ch in msg:
           if not ch.isalpha():
               result += ch
   
       return result
   

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