unittest in five minutes Ray Toal

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

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!

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 The unit testing chapter from Dive Into Python Are there alternatives to unittest? See what they say on StackOverflowSee what they say on StackOverflow

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]

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)

Write a stub (interleave.py) def interleave(a, b): return None

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)

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]

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)

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]

Rerun the test $ python interleavetest.py Ran 1 test in 0.000s OK

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