Writing Dumb Tests Luke Lee References: http://bit.ly/dumber_tests_pytx2014 

Luke Lee • Scientific Python/Desktop Visualization • Recovering C developer • @durden20 • lukelee.me • codrspace.com/durden References: http://bit.ly/dumber_tests_pytx2014 

The Last Day of a Sprint References: http://bit.ly/dumber_tests_pytx2014 

The Last Day of a Sprint References: http://bit.ly/dumber_tests_pytx2014 

Testing Woes References: http://bit.ly/dumber_tests_pytx2014 

Smart Tests • Too many details • Data • Too much software References: http://bit.ly/dumber_tests_pytx2014 

Smart Tests Too Many Details import collections entry = collections.namedtuple('entry', ['name', 'value', 'units']) def lines_to_tuples(filename): tuples = [] with open(filename, 'r') as file_obj: for line in file_obj: fields = line.split() tuples.append(entry(*fields)) return tuples References: http://bit.ly/dumber_tests_pytx2014 

Smart Tests Too Many Details def test_lines_to_tuples_1(): # Test.txt contains: # Height 60 in # Length 30 in filename = 'test.txt' test_tuples = lines_to_tuples(filename) with open(filename, 'r') as file_obj: for line, test_tuple in zip(file_obj, test_tuples): fields = line.split() assert entry(*fields) == test_tuple References: http://bit.ly/dumber_tests_pytx2014 

Smart Tests Too Many Details "We've fallen into a trap of testing that the code does what the code says it does, rather than testing functional behavior we care about." -- Daniel Pope, "Every mock.patch is a little smell" References: http://bit.ly/dumber_tests_pytx2014 

Smart Tests Data Your data is clean, users' data is gold standard References: http://bit.ly/dumber_tests_pytx2014 

Random Data References: http://bit.ly/dumber_tests_pytx2014 

Random Data Fails sometimes References: http://bit.ly/dumber_tests_pytx2014 

Smart Tests Too Much Software • Too easy to change • Too much cognitive overhead References: http://bit.ly/dumber_tests_pytx2014 

import unittest class TestSequenceFunctions(unittest.TestCase): def setUp(self): self.seq = range(10) def test_shuffle(self): # make sure the shuffled sequence does not lose any elements random.shuffle(self.seq) self.seq.sort() self.assertEqual(self.seq, range(10)) # should raise an exception for an immutable sequence self.assertRaises(TypeError, random.shuffle, (1,2,3)) def test_sample(self): with self.assertRaises(ValueError): random.sample(self.seq, 20) for element in random.sample(self.seq, 5): self.assertTrue(element in self.seq) References: http://bit.ly/dumber_tests_pytx2014 

import pytest @pytest.fixture(scope="module", params=["merlinux.eu", "mail.python.org"]) def smtp(request): smtp = smtplib.SMTP(request.param) def fin(): print ("finalizing %s" % smtp) smtp.close() request.addfinalizer(fin) return smtp References: http://bit.ly/dumber_tests_pytx2014 

Bugs hide in complexity References: http://bit.ly/dumber_tests_pytx2014 

Saved by the Tests References: http://bit.ly/dumber_tests_pytx2014 

Smart enough to find bugs but dumb enough to DEBUG References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests • Doctests • Data over code • Think goals, not implementation • Be brave References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests import doctest • Limited means simple References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests Data over code • Commit examples with real data • numpy.savetxt • StringIO References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests Data over code • difflib • filecmp • binary data References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests Goals, not implementation • Docs guide testing • Postpone code coverage References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests Goals, not implementation def test_lines_to_tuples_2(): # Test.txt contains: # Height 60 in # Length 30 in filename = 'test.txt' correct_tuples = [] correct_tuples.append(entry(name='Height', value='60', units='in')) correct_tuples.append(entry(name='Length', value='30', units='in')) test_tuples = lines_to_tuples(filename) assert correct_tuples == test_tuples References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests Goals, not implementation Embrace the experience of other people, people not schooled in the details of your implementation, you can learn how to make your work easier to absorb, and therefore more effective at what it's designed to do. -- Dave Winer, Early author of RSS software References: http://bit.ly/dumber_tests_pytx2014 

Be Brave! References: http://bit.ly/dumber_tests_pytx2014 

Dumb Tests Be Brave! import pytest @pytest.mark.parametrize("input,expected", [ ("3+5", 8), ("2+4", 6), ("6*9", 42), ]) def test_eval(input, expected): assert eval(input) == expected References: http://bit.ly/dumber_tests_pytx2014 

Use asserts References: http://bit.ly/dumber_tests_pytx2014 

Conclusion 1. Uses real world data 2. Focuses on goals not implementation details 3. Lowers cognitive oveheard with brave, simple code References: http://bit.ly/dumber_tests_pytx2014 

Write Boring Tests References: http://bit.ly/dumber_tests_pytx2014 

@durden20 www.lukelee.me codrspace.com/durden References: http://bit.ly/dumber_tests_pytx2014