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Testing in PythonFariz Dararifariz@cs.ui.ac.id

Testing vs DebuggingTesting:Checking whether our program works for a set of inputs.Debugging:Finding a bug in our program and fixing it.

Software Tester as a job (1/2)

Software Tester as a job (2/2)

Why testing?• Because your program is not perfect.• That is, because you (as a programmer) are not perfect.• Even a professional programmer sometimes writes a program thatstill contains bugs.• Don't use this as an excuse for you to write a program carelessly!!!• Testing can detect bugs earlier so your program won't be releasedto public with too many noticeable bugs!• However, your program passing some testing does not mean thatyour program is correct in general, it's just that your program iscorrect for the given test cases!• Still, tested code is much better than untested code!

Square area function (oops!)def square_area(x):return x**3

Square area function (oops!)def square_area(x):return x**3Let's test this code!

You test the function, manually>>> square_area(1)1So far so good, but...

You test the function, manually>>> square_area(1)1So far so good, but...>>> square_area(2)8The expected output is 4.So, your program is incorrect when input = 2.

Then you fix your functiondef square_area(x):return x**2

And you test again the function, manually>>> square_area(1)1So far so good...>>> square_area(2)4This was previously incorrect. Now we get it correct!

And you test again the function, manually>>> square_area(1)1So far so good...>>> square_area(2)4This was previously incorrect. Now we get it correct!But what about for other inputs (say when input is negative)?

Systematic ways of testing•doctest•unittest

doctest• Comes prepackaged with Python• Simple, you basically just have to include your testcases inside your function comment (= docstring)• from python.org:The doctest module searches for pieces of text thatlook like interactive Python sessions, and thenexecutes those sessions to verify that they workexactly as shown.

Square area (oops) with doctestimport doctestdef square_area(x):"""compute the area of a square>>> square_area(1)1>>> square_area(2)4"""return x**3if __name__ == "__main__":doctest.testmod()

Square area (oops) with doctest

Square area with doctestimport doctestdef square_area(x):"""compute the area of a square>>> square_area(1)1>>> square_area(2)4"""return x**2if __name__ == "__main__":doctest.testmod()

When there is no error, there is nothing to print!Square area with doctest

When there is no error, there is nothing to print!Exercise:(1) Add a testcase for negative inputs, which should return nothing(2) Fix the square area function to handle negative inputsSquare area with doctest

import doctestdef square_area(x):"""compute the area of a square>>> square_area(1)1>>> square_area(2)4>>> square_area(-1)"""if x < 0:return Nonereturn x**2if __name__ == "__main__":doctest.testmod()Square area with doctest

Exercise: Create a program and doctest tocompute the area of a rectangle

import doctestdef rectangle_area(x,y):"""compute the area of a rectangle>>> rectangle_area(1,1)1>>> rectangle_area(2,3)6>>> rectangle_area(-2,3)>>> rectangle_area(2,-3)>>> rectangle_area(100,200)20000"""if x < 0 or y < 0:return Nonereturn x*yif __name__ == "__main__":doctest.testmod()Exercise: Create a program and doctest tocompute the area of a rectangle

unittest• Comes prepackaged with Python• More extensive than doctest, you have to writeyour own, separate, testing code• As the name suggests, unit testing tests units orcomponents of the code. (= imagine that your code ismillions of lines, and you have to test it)

unittest for String methodsimport unittestclass TestStringMethods(unittest.TestCase):def test_upper(self):self.assertEqual('foo'.upper(), 'FOO')def test_isupper(self):self.assertTrue('FOO'.isupper())self.assertFalse('Foo'.isupper())def test_split(self):s = 'hello world'self.assertEqual(s.split(), ['hello', 'world'])if __name__ == '__main__':unittest.main()

Square area (oops) with unittestdef square_area(x):return x**3square_oops.pyimport unittestfrom square_oops import square_areaclass TestSquareArea(unittest.TestCase):def test_negative(self):self.assertEqual(square_area(-1), None)def test_positive(self):self.assertEqual(square_area(1),1)self.assertEqual(square_area(2),4)def test_positive_large(self):self.assertEqual(square_area(40),1600)if __name__ == '__main__':unittest.main()square_oops_test.py

Square area with unittestdef square_area(x):if x < 0: return Nonereturn x**2square.pyimport unittestfrom square import square_areaclass TestSquareArea(unittest.TestCase):def test_negative(self):self.assertEqual(square_area(-1), None)def test_positive(self):self.assertEqual(square_area(1),1)self.assertEqual(square_area(2),4)def test_positive_large(self):self.assertEqual(square_area(40),1600)if __name__ == '__main__':unittest.main()square_test.py

Exercise: Create a program and unittest tocompute the area of a rectangle

Rectangle area with unittestdef rectangle_area(x,y):if x < 0 or y < 0: return Nonereturn x*yrectangle.pyimport unittestfrom rectangle import rectangle_areaclass TestRectangleArea(unittest.TestCase):def test_negative(self):self.assertEqual(rectangle_area(-1,1), None)self.assertEqual(rectangle_area(1,-1), None)self.assertEqual(rectangle_area(-1,-1), None)def test_positive(self):self.assertEqual(rectangle_area(1,1),1)self.assertEqual(rectangle_area(2,3),6)def test_positive_large(self):self.assertEqual(rectangle_area(40,40),1600)self.assertEqual(rectangle_area(40,500),20000)if __name__ == '__main__':unittest.main()rectangle_test.py(you need to copy and paste the code!)

Test-Driven Development (TDD)• A method of software development to define testsbefore actually starting coding!• The tests define the desired behavior of the program.• In this way, you code with the mission to satisfy thetests!

TDD Stages1. Before writing any code, write test cases.2. Run the tests, this would surely fail since there is nocode yet.3. Make working code as minimum as possible to satisfythe tests.4. Run the tests, and check if your code passes. If not, fixyour code until you pass.5. Now, time to refactor (= clean) your code, make sure therefactored code passes the tests.6. Repeat 1-5 for other program features.

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