Testing in Python

Testing in Python is a huge topic!!!

Automated vs. Manual Testing

Manual

exploratory testing
- No plan
- King of manual tesing

Automated testing

Unit Tests vs. Integration Tests

Untegration testing - Testing multiple components in a chain (together)
Unit testing - Testing singe component (single unit of code)

Test Runners

unittest
nose or nose2
pytest

Unittests

Unittest has been built into the Python standard library since version 2.1.

Consists of test steps (test cases)
Consists of test assertions
- Tests are grouped as methods in Classes
- Use a series of special assertion methods

Example

# No need to pip install ...
import unittest


class TestSum(unittest.TestCase):

    def test_sum(self):
        self.assertEqual(sum([1, 2, 3]), 6, "Should be 6")

    def test_sum_tuple(self):
        self.assertEqual(sum((1, 2, 2)), 6, "Should be 6")

if __name__ == '__main__':
    unittest.main()

Nose2

nose is compatible with any tests written using the unittest framework and can be used as a drop-in replacement for the unittest test runner.

Install it

pip install nose2

pytest

pytest supports execution of unittest test cases.

Assertions

Assertion	Equivalent
.assertEqual(a, b)	a == b
.assertTrue(x)	bool(x) is True
.assertFalse(x)	bool(x) is False
.assertIs(a, b)	a is b
.assertIsNone(x)	x is None
.assertIn(a, b)	a in b
.assertIsInstance(a, b)	isinstance(a, b)

Run tests

python -m unittest test
# or
python -m unittest discover # discover and run test*.py in current directory

Success output

..
----------------------------------------------------------------------
Ran 2 tests in 0.001s

OK

Fail output

.F
======================================================================
FAIL: test_my_mean_1 (tests.TestSum)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\projects\_BELGIPRO\testing\tests.py", line 20, in test_my_mean_1
    self.assertEqual(result, 2)
AssertionError: 0.0 != 2

----------------------------------------------------------------------
Ran 2 tests in 0.001s

FAILED (failures=1)

Running tests from VSCode

press Ctrl+Shift+P and type tests

Choose Python: Configure Tests Type and choose unittest Choose test directory. In my case testing Chhose test files pattern. In my case test*.py

'Test' icon is now on your left pannel Now you can run, debug all your tests

Handling Expected Failures

What if we are waiting for the failue or error?

class TestMean(unittest.TestCase):
    # Other tests...
    def test_on_empty(self):
        data = []
        with self.assertRaises(ZeroDivisionError):
            result = my_mean(data)

Side effects

Executing a piece of code will change the environment:

- the attribute of a class
- a file on the filesystem
- value in a database
- ...

How to prevent (mitigate)

- Refactor to follow SRP
- Mock
- ...

Mock

unittest.mock (on python.org)

dvk-net/unit-tests