Writing and debugging code is hard, but testing shouldn't be. This talk will discuss common techniques for writing simpler tests that still exercise your production code while preventing you from spending time debugging test code.

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

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

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

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

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

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

7. 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

8. 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

9. 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

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

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

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

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

14. 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

15. 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

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

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

18. Smart enough to find bugs
but dumb enough to
DEBUGReferences: http://bit.ly/dumber_tests_pytx2014

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

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

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

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

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

24. 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

25. 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

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

27. 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

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

29. 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

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

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