This document discusses techniques for testing software in difficult environments, including: 1. Refactoring code into testable components and using mocking to replace dependencies that are hard to control, like network connections. 2. Setting up test databases in memory to isolate tests from the production database. 3. Using mocking frameworks to create fake objects, classes, and modules that replace real dependencies and allow tests to run independently. 4. An example shows mocking smtplib to test email sending without actually sending emails.

1. Testing in Hard to Reach Places
Lee Begg
Begg Digital

2. Overview
● Goals
● The module
● Refactoring
● SqlAlchemy tricks
● Mocking hard things
Code: http://github.com/llnz/kiwipycon2011testing
Slides: http://www.beggdigital.com/media/kiwipycon2011testing.pdf

3. Goals
● Make sure it works properly
● All the time
● In all conditions
● Unit testing to check
● Cover 100%
● Might still miss cases

4. Example module
def main():
'''Check the tripwire, email if the latest values have an RMS value over 2'''
session = model.Session()
values = session.query(model.MeasuredValue).order_by(model.MeasuredValue.desc()).limit(20).all()
totalsq = 0
for value in values:
totalsq += value.value**2
rms = math.sqrt(totalsq)
if rms > 2:
body = """Database trip wire has been tripped
RMS value was: %s
"""
subject = "Tripwire report %s" % datetime.date.today()
msg = MIMEText(body)
msg['Subject'] = '[DBTW] %s' % subject
msg['To'] = ','.join(settings.TO_ADDRESSES)
msg['From'] = settings.FROM_ADDRESS
server = smtplib.SMTP('localhost')
result = server.sendmail(settings.FROM_ADDRESS, settings.TO_ADDRESSES, msg.as_string())
if len(result) != 0:
print "sendmail failures: %s" % result
server.quit()

5. Refactoring
● Refactor out components to test
class RMSTest(unittest.TestCase):
'''Test the RMS calculations'''
def testRMSCalc(self): def calcRMS(values):
testvalues = [ totalsq = 0.0
([0], 0), for value in values:
([1], 1), totalsq += value**2
([2], 2),
([0, 0], 0), rms = math.sqrt(totalsq/len(values))
([1, 1], 1), return rms
([0] * 20, 0),
([1] * 20, 1),
([0, 0, 0, 1], 0.5),
([3, 1, 3, 0, 1], 2),
]
for values, expected in testvalues:
result = tripwire.calcRMS(values)
self.assertAlmostEqual(result, expected, msg='rmsCalc(%s) gave %s,
expected %s' % (values, result, expected))

6. SqlAlchemy Tricks
● Change the database in the unittest setUp
method
● Done internally by Django
#override database setting
from dbtripwire import settings
settings.DATABASE_URL = 'sqlite:///:memory:'
from dbtripwire.model import initDatabase, dropDatabase

7. SqlAlchemy Tricks
class DatabaseTestSetup(object):
'''Create the database in the setUp, and drop it in tearDown
Used to abstract this away from all the unittests that use the Database.
Must be the first class inherited from, or TestCase will override these
methods, not the other way around.
'''
def setUp(self):
'''Initialise the database with the tables'''
initDatabase()
def tearDown(self):
'''Drop the tables'''
dropDatabase()

8. SqlAlchemy Tricks
class ModelTest(DatabaseTestSetup, unittest.TestCase):
'''Test the model classes'''
def testMeasuredValueTable(self):
'''MeasuredValue table test'''
session = model.Session()
self.assertEqual(session.query(model.MeasuredValue).count(), 0)
mv = model.MeasuredValue(5)
self.assert_(mv)
session.add(mv)
session.commit()
self.assertEqual(session.query(model.MeasuredValue).count(), 1)
mv1 = session.query(model.MeasuredValue).one()
self.assertEqual(mv1.id, 1)
self.assertEqual(mv1.value, 5)
#don't forget to test the __repr__ string
self.assertEqual(repr(mv1), "<MeasuredValue(1, 5)>")
session.delete(mv1)
session.commit()
self.assertEqual(session.query(model.MeasuredValue).count(), 0)

9. Mock
● Creating fake “mock” objects/classes/modules
● Replace things you couldn't normally control
● A few frameworks available
● Very useful in replacing network connections
● Httplib for example
● Smtplib for another

10. Mock example
class SendEmailTest(unittest.TestCase):
'''Test sending email'''
def testSendEmail(self):
tt = minimock.TraceTracker()
smtpconn = minimock.Mock('smtplib.SMTP', tracker=tt)
minimock.mock('smtplib.SMTP', mock_obj=smtpconn)
smtpconn.mock_returns = smtpconn
smtpconn.sendmail.mock_returns = {}
tripwire.sendEmail(2.5, datetime.date(2011, 8, 16))
expected = r"""Called smtplib.SMTP('localhost')
Called smtplib.SMTP.sendmail(
'lee@beggdigital.co.nz',
['lee@beggdigital.co.nz', 'llnz@paradise.net.nz'],
'Content-Type: text/plain; charset="us-ascii"nMIME-Version: 1.0nContent-Transfer-Encoding:
7bitnSubject: [DBTW] Tripwire Report 2011-08-16nTo: lee@beggdigital.co.nz,
llnz@paradise.net.nznFrom: lee@beggdigital.co.nznnDatabase trip wire has been tripped.nnRMS
value was: 2.5n')
Called smtplib.SMTP.quit()"""
self.assertTrue(tt.check(expected), tt.diff(expected))
minimock.restore()