Unit Testing in Python

sample.py

import unittest

class Storage:
    def __init__(self, capacity):
        self.capacity = capacity
        self.values = []
        
    def add(self, val):
        self.values.append(val)
        
    def size(self):
        return len(self.values)
        
    def __iter__(self):
        return iter(self.values)
    
class StorageTests(unittest.TestCase):
    def setUp(self):
        self.db = Storage(3)
        
    def testEmpty(self):
        self.assertEqual(self.db.size(), 0)
    
    def testOneElement(self):
        self.db.add(10)
        self.assertEqual(self.db.size(), 1)
        for item in self.db:
            self.assertEqual(10, item)
            
    def testThreeElements(self):
        nums = [10, 20, 30]
        
        for num in nums:
            self.db.add(num)

        self.assertEqual(self.db.size(), len(nums))
        
        index = 0
        for item in self.db:
            self.assertEqual(nums[index], item)
            index += 1
            
    def testBeyondIter(self):
        nums = [10, 20, 30]
        
        for num in nums:
            self.db.add(num)

        self.assertEqual(self.db.size(), len(nums))
        
        index = 0
        iteration = iter(self.db)
        item = 0
        while True:
            item = next(iteration, None)
            if item is None:
                break
            self.assertEqual(item, nums[index])
            index += 1
        item = next(iteration, None)
        self.assertEqual(item, None)

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

Unit Testing in Python.md

• A testcase is created by subclassing unittest.TestCase.
• Individual tests are defined with methods whose names start with the letters "test". This naming convention informs the test runner about which methods represent tests.
• Following is a typical example of unit test:

# PythonUnitTest.py

import unittest

class Sort(unittest.TestCase):
    def setUp(self):
        self.nums = [10,20,30,40]

    def tearDown(self):
        self.nums = None

    def test_blank(self):
        self.nums = None
        self.assertEqual(self.nums, None)
        
    def test_len(self):
        self.assertEqual(len(self.nums), 4)

    def test_contains(self):
        self.assertTrue(10 in self.nums)
        self.assertTrue(20 in self.nums)
        self.assertTrue(30 in self.nums)
        self.assertTrue(40 in self.nums)
        self.assertIn(40, self.nums)
        self.assertNotIn(60, self.nums)

def main():
    unittest.main()

if __name__ == '__main__':
    main()

Execute the tests like this: python PythonUnitTest.py --verbose

Skipping Test Cases

@unittest.skip("demonstrating skipping")
    def test_nothing(self):
        self.fail("shouldn't happen")

Assert Methods

• assertEqual(a, b)
• assertNotEqual(a, b)
• assertTrue(x)
• assertFalse(x)
• assertIs(a, b)
• assertIsNot(a, b)
• assertIsNone(x)
• assertIsNotNone(x)
• assertIn(a, b)
• assertNotIn(a, b)
• assertIsInstance(a, b)
• assertNotIsInstance(a, b)
• assertGreater(a, b)
• assertGreaterEqual
• assertLess
• assertLessEqual
• assertRegexpMatches(s, r)
• assertItemsEqual(a, b)
• assertDictContainsSubset(a, b)

Useful Links

• https://docs.python.org/2/library/unittest.html
• Python Unit Testing - Basic Tutorial
• Test-Driven Development in Python - O'Reilly Media