Automated Software Testing

Automated Software Testing
Arild Nilsen, May 2016

• Introduction
• Dependency Injection
• Tips & Tricks

automated software testing
test-driven development (TDD)
vs.
software tester
vs.

integration test
unit test system test
acceptance test
end-to-end test
A/B test

Should you write tests?
- Truth about booking.com
“Booking is destroying my career (…)
I am not allowed to write tests”
“I don’t do tests”
- David Thomas
A/B testing
Some unit tests
Very experienced
Writes tests for complex algorithm

Benefits of automated tests
• Catch regression errors
• Drives the design of the code
• Serves as documentation

class Poller:
def __init__(self):
self.service = Service()
def wait_for_completed(self):
while not self.service.is_done():
sleep(10)
Poller().wait_for_completed()

class Poller:
def __init__(self, service, poll_delay):
self.service = service
self.poll_delay = poll_delay
sleep(self.poll_delay)
Poller(Service(), 10).wait_for_completed()

class Poller:
def set_service(self, service):
self.service = service
def set_poll_delay(self, poll_delay):
poller = Poller()
poller.set_service(Service())
poller.set_poll_delay(10)
poller.wait_for_completed()

class ServiceMock(Service):
def __init__(self):
self.called = 0
def is_done(self):
self.called += 1
return self.called == 2
def terminates_when_service_is_done():
mock = ServiceMock()
Poller(mock, 0).wait_for_completed()
assert 2 is mock.called

mock = Mock(Service)
when(mock.is_done())
.thenReturn(False)
.thenReturn(True)
Poller(mock, 0).wait_for_completed()
verify(mock, times(2)).is_done()

class Poller(Service):
def __init__(self, poll_delay):
while not self.is_done():

class PollerTest(Poller):
def __init__(self, poll_delay):
super(PollerTest,self)
.__init__(poll_delay)
self.called = 0
def is_done(self):
self.called += 1
return self.called == 2
poller = PollerTest(poll_delay=0)
poller.wait_for_completed()
assert 2 is poller.called

Things that makes testing
harder
• Inheritance
• Static methods
• Global state
• Mixing of concerns
• Top 10 things which make your code hard to
test

See the test fail
• Does it actually fail?
• Is the error message descriptive?

@Test
public void readsFile() throws VodFileStorageException {
try (InputStream stream = new InputStream("clip.mp4")) {
ftpFileStorage.writeFile("tmp.mp4", stream);
}
try (InputStream expected = new InputStream("clip.mp4"))) {
InputStream actual = ftpFileStorage.readFile("tmp.mp4");
contentEquals(expected, actual);
}
}
@Test
public void readsFile() throws VodFileStorageException {
try (InputStream stream = new InputStream("clip.mp4")) {
ftpFileStorage.writeFile("tmp.mp4", stream);
}
try (InputStream expected = new InputStream("clip.mp4"))) {
InputStream actual = ftpFileStorage.readFile("tmp.mp4");
assertThat(contentEquals(expected, actual), is(true));
}
}

Naming and structuring tests
• Test features over methods
• Some duplication is fine, but test should read
well

@Mock
FolderWatchService service;
@Test
public void addsJobId() throws Exception {
FolderWatch folderWatch = createFolderWatch()
.jobIds(newHashSet())
.build();
JobId id1 = createJob().build().getId();
JobId id2 = createJob().build().getId();
folderWatch.addJobId(service, id1);
verify(service).addJobId(folderWatch.getId(), id1);
assertThat(folderWatch.getJobIds(), is(newHashSet(id1)));
folderWatch.addJobId(service, id2);
verify(service).addJobId(folderWatch.getId(), id2);
assertThat(folderWatch.getJobIds(), is(newHashSet(id1, id2)));
}

Scope of test
Writing Great Unit Tests:
Best and Worst Practice
- Steve Sanderson, 2009

Testing too much
• And’s , Or’s or But’s
• Too many mocks

Where to learn more?
Inversion of Control Containers
and the Dependency Injection
pattern
- Martin Fowler, 2004
Writing Great Unit Tests:
Best and Worst Practice
- Steve Sanderson, 2009

Automated Software Testing

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