After reading lesson 36, you’ll be able to
- Use the unittest library
- Write tests for your program
- Efficiently debug your programs
It’s unlikely that you’ll write a perfect program on the first try. Often you’ll write code, test it with a few inputs, make changes to it, and test it again, repeating this process until your program runs as expected.
Consider this
Think about your experience in programming so far. When you write a program and it doesn’t work, what kinds of things do you do to fix it?
Answer:
Look at the error message, if any, and see whether there are clues like line numbers that can direct me toward the issue. Put print statements at certain locations. Try a different input.
Python has many libraries that can help you create a testing structure around your program. A testing library is especially useful when you have programs that contain different functions. One testing library comes with your Python installation, and its documentation for Python 3.5 is available at https://docs.python.org/3.5/library/unittest.html.
To create a suite of tests, you create a class representing that suite. Methods inside that class represent different tests. Every test that you want to run should have test_ as a prefix, and then any name for the method. The following listing contains code that defines two simple tests and then runs them.
Listing 36.1. Simple test suite
import unittest #1
class TestMyCode(unittest.TestCase): #2
def test_addition_2_2(self): #3
self.assertEqual(2+2, 4) #4
def test_subtraction_2_2(self): #5
self.assertNotEqual(2-2, 4) #6
unittest.main() #7
The code prints the following:
Ran 2 tests in 0.001s OK
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def test_addition_2_2(self):
self.assertEqual(2+2, 5)
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FAIL: test_addition_2_2 (__main__.TestMyCode)
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:/Users/Ana/.spyder-py3/temp.py", line 5, in test_addition_2_2
self.assertEqual(2+2, 5)
AssertionError: 4 != 5
----------------------------------------------------------------------
Ran 2 tests in 0.002s
FAILED (failures=1)
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- Mjzdb rrkz etuis dfelai: TestMyCode
- Mgjps rrcx ildfae: test_addition_2_2
- Mapju fjon desnii rop zror ielafd: self.assertEqual(2+2, 5)
- Mpq jr idlfea, pq agmncriop rwcp veual rj reb ncg brzw alevu rj epcedetx: 4 != 5
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Listing 36.2. File, named funcs.py, containing functions to test
def is_prime(n):
prime = True
for i in range(1,n):
if n%i == 0:
prime = False
return prime
def absolute_value(n):
if n < 0:
return -n
elif n > 0:
return n
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Definition
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Listing 36.3. File, named test.py, containing the tests
import unittest #1
import funcs #2
class TestPrime(unittest.TestCase): #3
def test_prime_5(self): #4
isprime = funcs.is_prime(5) #5
self.assertEqual(isprime, True) #6
def test_prime_4(self):
isprime = funcs.is_prime(4)
self.assertEqual(isprime, False)
def test_prime_10000(self):
isprime = funcs.is_prime(10000)
self.assertEqual(isprime, False)
class TestAbs(unittest.TestCase):
def test_abs_5(self):
absolute = funcs.absolute_value(5)
self.assertEqual(absolute, 5)
def test_abs_neg5(self):
absolute = funcs.absolute_value(-5)
self.assertEqual(absolute, 5)
def test_abs_0(self):
absolute = funcs.absolute_value(0)
self.assertEqual(absolute, 0)
unittest.main()
FAIL: test_abs_0 (__main__.TestAbs)
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:/Users/Ana/test.py", line 24, in test_abs_0
self.assertEqual(absolute, 0)
AssertionError: None != 0
======================================================================
FAIL: test_prime_5 (__main__.TestPrime)
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:/Users/Ana/test.py", line 7, in test_prime_5
self.assertEqual(isprime, True)
AssertionError: False != True
----------------------------------------------------------------------
Ran 6 tests in 0.000s
FAILED (failures=2)
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Thinking like a programmer
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Quick check 36.3
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To check that two dictionaries are equal
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----> 1 import unittest
2 import funcs
3
4 class TestPrime(unittest.TestCase):
5 def test_prime_5(self):
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21 self.assertEqual(absolute, 5)
22 def test_abs_0(self):
1--> 23 absolute = funcs.absolute_value(0)
24 self.assertEqual(absolute, 0)
25
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6 return prime
7
----> 8 def absolute_value(n):
9 if n < 0:
10 return -n
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9 if n < 0:
10 return -n
---> 11 elif n > 0:
12 return n
13
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Quick check 36.4
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In this lesson, my goal was to teach you the basics of testing and debugging and to give you more practice at importing and using libraries. I showed you how to use the unittest library to organize your tests and the importance of separating the code from the testing framework. You used a debugger to step through your code.
Here’s a buggy program. Write unit tests and try to debug it:
def remove_buggy(L, e):
"""
L, list
e, any object
Removes all e from L.
"""
for i in L:
if e == i:
L.remove(i)