Python Unit Test Automation

Listing 6-5.  test_module01.py
from calculator import Calculator
import pytest
class TestClass01:
        def test_case01(self):
                calc = Calculator()
                result = calc.add(2, 2)
                assert 4 == result
        def test_case02(self):
                with pytest.raises(ValueError):
                        result = Calculator().add(2, 'two')
In the modified code shown in Listing 
6-5
, we’re trying to add an integer and a string, 
which should raise a ValueError exception.

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Chapter 6 
■
 tips and triCks
106
If you run the modified test module, you get the following:
============================= 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 2 items
test_module01.py::TestClass01::test_case01 PASSED
test_module01.py::TestClass01::test_case02 FAILED
================================= FAILURES ====================================
__________________________ TestClass01.test_case02 ____________________________
self =
    def test_case02(self):
            with pytest.raises(ValueError):
>                   result = Calculator().add(2, 'two')
test_module01.py:14:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
self = , x = 2, y = 'two'
    def add(self, x, y):
>           return x+y
E           TypeError: unsupported operand type(s) for +: 'int' and 'str'
calculator.py:4: TypeError
===================== 1 failed, 1 passed in 0.33 seconds ======================
As you can see in the output, the second test fails as it does not detect a ValueError 
exception. So, let’s add the provision to check if both the arguments are numeric, else 
raise a ValueError exception—see Listing 
6-6
.