unittest in 5 minutes
Download as PPTX, PDF1 like1,864 views
This document discusses unit testing in Python. It provides an example of writing a test-driven function that interleaves two lists. The steps shown are: 1. Write test cases for the interleave function before writing the code. This tests various input/output cases. 2. Create a stub interleave function that returns None to make the tests fail as expected. 3. Write the interleave code using itertools.izip_longest to zip the lists together. 4. Rerun the tests to ensure they now pass with the implemented function.
![A first example
• Let's write a function to interleave two lists
• It will be okay if one list is longer than the
other
• Before we start writing the code, we should
know what the function should produce for all
types of inputs:
interleave([], []) ☞ []
interleave([1,5,3], ["hello"]) ☞
[1,"hello",5,3]
interleave([True], [[], 8]) ☞ [True, [],
8]](https://image.slidesharecdn.com/unittest-120108140111-phpapp02/85/unittest-in-5-minutes-5-320.jpg)
![Write the test first(interleavetest.py)
from interleave import interleave
import unittest
class TestGettingStartedFunctions(unittest.TestCase):
def test_interleave(self):
cases = [
([], [], []),
([1, 4, 6], [], [1, 4, 6]),
([], [2, 3], [2, 3]),
([1], [9], [1, 9]),
([8, 8, 3, 9], [1], [8, 1, 8, 3, 9]),
([2], [7, 8, 9], [2, 7, 8, 9]),
]
for a, b, expected in cases:
self.assertEqual(interleave(a, b), expected)](https://image.slidesharecdn.com/unittest-120108140111-phpapp02/85/unittest-in-5-minutes-6-320.jpg)
![Run the test
$ python interleavetest.py
F
======================================================================
FAIL: test_interleave (__main__.TestGettingStartedFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
File "interleavetest.py", line 15, in test_interleave
self.assertEqual(interleave(a, b), expected)
AssertionError: None != []
----------------------------------------------------------------------
Ran 1 test in 0.000s
FAILED (failures=1)](https://image.slidesharecdn.com/unittest-120108140111-phpapp02/85/unittest-in-5-minutes-8-320.jpg)
![Now write the code
def interleave(a, b):
"""Return the interleaving of two sequences as a list."""
return [y for x in izip_longest(a, b) for y in x if y is not None]](https://image.slidesharecdn.com/unittest-120108140111-phpapp02/85/unittest-in-5-minutes-9-320.jpg)
![Test again
$ python interleavetest.py
E
======================================================================
ERROR: test_interleave (__main__.TestGettingStartedFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
File "interleavetest.py", line 15, in test_interleave
self.assertEqual(interleave(a, b), expected)
File "/Users/raytoal/scratch/interleave.py", line 3, in interleave
return [y for x in izip_longest(a, b) for y in x if y is not None]
NameError: global name 'izip_longest' is not defined
----------------------------------------------------------------------
Ran 1 test in 0.000s
FAILED (errors=1)](https://image.slidesharecdn.com/unittest-120108140111-phpapp02/85/unittest-in-5-minutes-10-320.jpg)
![Fix the code
from itertools import izip_longest
def interleave(a, b):
"""Return the interleaving of two sequences as a list."""
return [y for x in izip_longest(a, b) for y in x if y is not None]](https://image.slidesharecdn.com/unittest-120108140111-phpapp02/85/unittest-in-5-minutes-11-320.jpg)
unittest in 5 minutes
- 1. unittest in five minutes Ray Toal 2011-10-22
- 2. How to unit test • Not manually, that's for sure • You write code that exercises your code • Perform assertions that record o that you get the results you expect for various inputs o that exceptions are raised when they should be • Pay attention to edge cases
- 3. Test-driven development • Write some tests (yes, first) • Run them o They will fail because the code isn't written yet. That is supposed to happen. Good news is you will know the tests run. • Write some code • Now run the tests again • Work until the tests pass • Iterate!
- 4. Unit testing in Python • The module unittest is already there • Docs • Python 2.7 • Python 3 • Also see • The unit testing chapter from Dive Into Python • Are there alternatives to unittest? See what they say on StackOverflow
- 5. A first example • Let's write a function to interleave two lists • It will be okay if one list is longer than the other • Before we start writing the code, we should know what the function should produce for all types of inputs: interleave([], []) ☞ [] interleave([1,5,3], ["hello"]) ☞ [1,"hello",5,3] interleave([True], [[], 8]) ☞ [True, [], 8]
- 6. Write the test first(interleavetest.py) from interleave import interleave import unittest class TestGettingStartedFunctions(unittest.TestCase): def test_interleave(self): cases = [ ([], [], []), ([1, 4, 6], [], [1, 4, 6]), ([], [2, 3], [2, 3]), ([1], [9], [1, 9]), ([8, 8, 3, 9], [1], [8, 1, 8, 3, 9]), ([2], [7, 8, 9], [2, 7, 8, 9]), ] for a, b, expected in cases: self.assertEqual(interleave(a, b), expected)
- 7. Write a stub (interleave.py) def interleave(a, b): return None
- 8. Run the test $ python interleavetest.py F ====================================================================== FAIL: test_interleave (__main__.TestGettingStartedFunctions) ---------------------------------------------------------------------- Traceback (most recent call last): File "interleavetest.py", line 15, in test_interleave self.assertEqual(interleave(a, b), expected) AssertionError: None != [] ---------------------------------------------------------------------- Ran 1 test in 0.000s FAILED (failures=1)
- 9. Now write the code def interleave(a, b): """Return the interleaving of two sequences as a list.""" return [y for x in izip_longest(a, b) for y in x if y is not None]
- 10. Test again $ python interleavetest.py E ====================================================================== ERROR: test_interleave (__main__.TestGettingStartedFunctions) ---------------------------------------------------------------------- Traceback (most recent call last): File "interleavetest.py", line 15, in test_interleave self.assertEqual(interleave(a, b), expected) File "/Users/raytoal/scratch/interleave.py", line 3, in interleave return [y for x in izip_longest(a, b) for y in x if y is not None] NameError: global name 'izip_longest' is not defined ---------------------------------------------------------------------- Ran 1 test in 0.000s FAILED (errors=1)
- 11. Fix the code from itertools import izip_longest def interleave(a, b): """Return the interleaving of two sequences as a list.""" return [y for x in izip_longest(a, b) for y in x if y is not None]
- 12. Rerun the test $ python interleavetest.py . ------------------------------------------------------------- Ran 1 test in 0.000s OK
- 13. kthx