Python Unit Test Automation

Listing 6-2.  calculator.py
class Calculator:
        def add(self, x, y):
               pass
Make sure that there are no errors in calculator.py by running the following 
command every time you modify the module:
python3 calculator.py
Now import Calculator in the test module, as shown in Listing 
6-3
.
Listing 6-3.  test_module01.py
from calculator import Calculator
class TestClass01:
        def test_case01(self):
               calc = Calculator()
               result = calc.add(2, 2)
               assert 4 == result
Run the test_module01.py again. The output will be as follows:
============================ test session starts ==============================
platform linux -- Python 3.4.2, pytest-3.0.4, py-1.4.31, pluggy-0.4.0 --  
/usr/bin/python3
cachedir: .cache
rootdir: /home/pi/book/code/chapter06, inifile:
collected 1 items
test_module01.py::TestClass01::test_case01 FAILED
================================= FAILURES ====================================
___________________________ TestClass01.test_case01 ___________________________
self =
    def test_case01(self):
            calc = Calculator()
            result = calc.add(2, 2)
>           assert 4 == result
E           assert 4 == None
test_module01.py:9: AssertionError
=========================== 1 failed in 0.32 seconds ==========================

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Chapter 6 
■
 tips and triCks
105
The add() method returns the wrong value (i.e., pass), as it does not do anything at 
the moment. Fortunately, pytest returns the line with the error in the test run so you can 
decide what you need to change. Let’s fix the code in the add() method in calculator.py 
as shown in Listing 
6-4
.