Unit testing for those seeking instant gratification - Maciej Bliziński Abstract: Unit testing has long term benefits. However, depending on how you use it, it can have short term benefits too. This is an introductory talk, aimed at both beginner and experienced Python programmers who would like to get started testing their code.

1. Unit testing
For those seeking instant
gratification
Maciej Bliziński <blizinski@google.com>
Python Ireland 2010-11-10

2. Helps the design
Provides live documentation
Helps refactoring

3. But I'm hungry right now!

4. I love to see my code run

6. task: Index a list of dictionaries by one of the fields
def IndexBy(d_list, field_name):
result = {}
for d in d_list:
result[d[field_name]] = d
return result

7. def MakePackageNameBySoname(soname): (continued...)
"""Find the package name based on the soname.
for key in parsed:
Returns a pair of pkgname, catalogname. if parsed[key]:
""" keywords_pkgname[key] = SonameToStringWithChar(parsed[key], "-")
def AddSeparator(d, sep): keywords_catalogname[key] = SonameToStringWithChar(parsed[key], "_")
"""Adds a separator based on the neighboring else:
of two digits.""" keywords_pkgname[key] = ""
dc = copy.copy(d) keywords_catalogname[key] = ""
if dc["version"]: pkgname_list = []
if (dc["basename"][-1].isdigit() keywords_pkgname = AddSeparator(keywords_pkgname, "-")
and pkgname_list.append(
dc["version"][0].isdigit()): "CSW%(basename)s%(sep)s%(version)s" % keywords_pkgname)
dc["sep"] = sep keywords_catalogname = AddSeparator(keywords_catalogname, "_")
else: catalogname_list = [
dc["sep"] = "" "%(basename)s%(sep)s%(version)s" % keywords_catalogname,
else: ]
dc["sep"] = "" return pkgname_list, catalogname_list
return dc
soname_re = re.compile(r"(?P<basename>[w+]+([.-]+[w+]+)*)"
r".so"
r"(.(?P<version>[d.]+))?"
r"$")
m = soname_re.match(soname)
if not m:
# There was no ".so" component, so it's hardo to figure out which one is
# the name, but we'll try to figure out the numeric part of the soname.
digits = "".join(re.findall(r"[0-9]+", soname))
alnum = "".join(re.findall(r"[a-zA-Z]+", soname))
parsed = {
"basename": alnum,
"version": digits,
}
else:
parsed = m.groupdict()
keywords_pkgname = {}
keywords_catalogname = {}
Real life example

8. task: Index a list of dictionaries by one of the fields
def IndexBy(d_list, field_name):
result = {}
for d in d_list:
result[d[field_name]] = d
return result

9. import example_1
def main():
d = [{"foo": "a", "bar": "b"},
{"foo": "c", "bar": "d"}]
print example_1.IndexBy(d, "foo")
if __name__ == '__main__':
main()

10. import unittest
import example_1
import pprint
class IndexByUnitTest(unittest.TestCase):
def testTwoElements(self):
d = [{"foo": "a", "bar": "b"},
{"foo": "c", "bar": "d"}]
pprint.pprint(example_1.IndexBy(d, "foo"))
if __name__ == '__main__':
unittest.main()

11. import unittest
import example_1
class IndexByUnitTest(unittest.TestCase):
def testTwoElements(self):
d = [{"foo": "a", "bar": "b"},
{"foo": "c", "bar": "d"}]
expected = {
'a': {'foo': 'a', 'bar': 'b'},
'c': {'foo': 'c', 'bar': 'd'},
}
self.assertEquals(expected, example_1.IndexBy(d, "foo"))
if __name__ == '__main__':
unittest.main()

12. blizinski@workstation ~/unit-test-talk $ python2.6 example_1_test.py
.
----------------------------------------------------------------------
Ran 1 test in 0.000s
OK

13. Cultured way of playing with code

14. Changing your code

15. import unittest
import example_1
class IndexByUnitTest(unittest.TestCase):
def testTwoElements(self):
d = [{"foo": "a", "bar": "b"},
{"foo": "c", "bar": "d"},
{"foo": "c", "bar": "e"}]
expected = {
'a': {'foo': 'a', 'bar': 'b'},
'c': {'foo': 'c', 'bar': 'd'},
}
self.assertEquals(expected, example_1.IndexBy(d, "foo"))
if __name__ == '__main__':
unittest.main()

17. task: Index a list of dictionaries by one of the fields
def IndexBy(d_list, field_name):
result = {}
for d in d_list:
result.setdefault(d[field_name], [])
result[d[field_name]].append(d)
return result

18. Keeping a track record

19. def testMakePackageNameDashesNoDashes(self):
soname = "libpyglib-2.0-python.so.0"
expected = (
['CSWlibpyglib2-0python0'],
['libpyglib2_0python0'],
)
self.assertEqual(expected,
su.MakePackageNameBySoname(soname))
def testMakePackageNameDashesNoDashesPython(self):
soname = "libpython3.1.so.1.0"
expected = (
['CSWlibpython3-1-1-0'],
['libpython3_1_1_0'],
)
self.assertEqual(expected,
su.MakePackageNameBySoname(soname))

20. The trust issue
Your first steps in unit testing

21. Hug me, I only look alien!
(never mind my boxing gloves)

23. It's about the way
pieces of code
fit together

24. Your trust will gradually shift

25. Part of the development process

26. It's a tool which helps with
some of the everyday tasks.

27. Further reading
http://en.wikipedia.org/wiki/Unit_testing
http://diveintopython.org/unit_testing/index.html
Mock objects, stubs and fakes
Contact
Maciej Bliziński <blizinski@google.com>

28. References
Images:
http://commons.wikimedia.org/wiki/File:Pantheon_rome_inside_1-muniu.jpg by Muniu
http://commons.wikimedia.org/wiki/File:Instant_miso_soup.jpg by Gleam
http://www.flickr.com/photos/f-oxymoron/4203860207/sizes/l/in/photostream/ by f-oxymoron
http://www.flickr.com/photos/jurvetson/1381322008/sizes/l/in/photostream/ by jurvetson
http://www.flickr.com/photos/7332902@N05/3221210836/ by David O'Driscoll
http://www.flickr.com/photos/edsweeney/4212380812/sizes/o/in/photostream/ by Ed Sweeney
http://www.flickr.com/photos/jenny-pics/3230153121/sizes/l/in/photostream/ by jenny downing
http://www.flickr.com/photos/oskay/265899766/ by Windell Oskay
http://www.flickr.com/photos/alismith44/357361903/ by Ali West
http://www.flickr.com/photos/cezaryborysiuk/3947857278/ by Cezary Borysiuk
http://www.flickr.com/photos/wilhei/109403331/ by wilhei55
http://www.flickr.com/photos/antonymayfield/3221876089/ by antony_mayfield
http://www.flickr.com/photos/ralphandjenny/4999895776/ by Ralph Daily