learn-python/contrib/advanced-python/unittest_in_python.md

Unittest in Python

The unittest module in Python is a powerful and flexible framework for writing and running tests. It provides a range of tools for constructing and running tests, making it easier to ensure your code behaves as expected.

Writing Tests

A typical test case is created by subclassing unittest.TestCase and defining methods that start with test.

Example: Basic Test Case

import unittest

class 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'])
        with self.assertRaises(TypeError):
            s.split(2)

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

Output

When you run this script, the output will be:

...
----------------------------------------------------------------------
Ran 3 tests in 0.001s

OK

Running Tests

You can run tests by calling the script directly. When executed, unittest will find all test cases and run them:

python test_script.py

Alternatively, you can use the command line to discover and run tests:

python -m unittest discover

Test Fixtures

Test fixtures are used to set up a known state for tests and clean up afterward. You can use setUp() and tearDown() methods for this purpose.

Example: Test Fixtures

import unittest

class TestExample(unittest.TestCase):

    def setUp(self):
        self.number = 42

    def tearDown(self):
        del self.number

    def test_addition(self):
        self.assertEqual(self.number + 10, 52)

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

Output

.
----------------------------------------------------------------------
Ran 1 test in 0.000s

OK

Organizing Tests

Tests can be organized into test suites to run them collectively. This is useful for running related tests together.

Example: Test Suites

import unittest

class TestMath(unittest.TestCase):

    def test_add(self):
        self.assertEqual(1 + 1, 2)

    def test_subtract(self):
        self.assertEqual(5 - 3, 2)

class TestString(unittest.TestCase):

    def test_upper(self):
        self.assertEqual('foo'.upper(), 'FOO')

    def test_isupper(self):
        self.assertTrue('FOO'.isupper())

if __name__ == '__main__':
    suite = unittest.TestSuite()
    suite.addTests(unittest.makeSuite(TestMath))
    suite.addTests(unittest.makeSuite(TestString))
    runner = unittest.TextTestRunner()
    runner.run(suite)

Output

....
----------------------------------------------------------------------
Ran 4 tests in 0.001s

OK

Assertions

unittest provides a wide range of assertion methods to verify conditions in tests:

• assertEqual(a, b): Check a == b
• assertNotEqual(a, b): Check a != b
• assertTrue(x): Check bool(x) is True
• assertFalse(x): Check bool(x) is False
• assertIs(a, b): Check a is b
• assertIsNot(a, b): Check a is not b
• assertIsNone(x): Check x is None
• assertIsNotNone(x): Check x is not None
• assertIn(a, b): Check a in b
• assertNotIn(a, b): Check a not in b
• assertIsInstance(a, b): Check isinstance(a, b)
• assertNotIsInstance(a, b): Check not isinstance(a, b)

Example: Using Assertions

import unittest

class TestAssertions(unittest.TestCase):

    def test_assert_equal(self):
        self.assertEqual(3 + 2, 5)

    def test_assert_true(self):
        self.assertTrue('FOO'.isupper())

    def test_assert_in(self):
        self.assertIn('h', 'hello')

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

Output

...
----------------------------------------------------------------------
Ran 3 tests in 0.001s

OK

The unittest module is a powerful framework that provides all the tools necessary to write comprehensive and maintainable tests. By leveraging its features, you can ensure your code works correctly and prevent regressions, ultimately leading to more robust and reliable software.