Writing good code is hard, or at least it can be. A major challenge is to ensure that your code remains correct as you add new functionality.
Unit testing is a modern, light-weight testing methodology in widespread use in many programming languages. Development that relies on unit tests is often referred to as Test-Driven Development (TDD). Most Twisted code is tested using TDD.
To gain a solid understanding of unit testing in Python, you should read the unittest -- Unit testing framework chapter of the Python Library Reference. There is also a ton of information available online and in books.
Introductory example of Python unit testing
This document is principally a guide to Trial, Twisted's unit testing framework. Trial is based on Python's unit testing framework. While we do not aim to give a comprehensive guide to general Python unit testing, it will be helpful to consider a simple non-networked example before expanding to cover a networking code that requires the special capabilities of Trial. If you are already familiar with unit test in Python, jump straight to the section specific to testing Twisted code.
_N
(where the N
are successive
integers) to file names to keep them separate. This is a minor visual
distraction that should be ignored.Creating an API and writing tests
We'll create a library for arithmetic calculation. First, create a
project structure with a directory called calculus
containing an empty __init__.py
file.
Then put the following simple class definition API into calculus/base_1.py
:
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# -*- test-case-name: calculus.test.test_base_1 -*- class Calculation(object): def add(self, a, b): pass def subtract(self, a, b): pass def multiply(self, a, b): pass def divide(self, a, b): pass
(Ignore the test-case-name
comment for
now. You'll see why that's useful below.)
We've written the interface, but not the code. Now we'll write a set of tests. At this point of development, we'll be expecting all tests to fail. Don't worry, that's part of the point. Once we have a test framework functioning, and we have some decent tests written (and failing!), we'll go and do the actual development of our calculation API. This is the preferred way to work for many people using TDD - write tests first, make sure they fail, then do development. Others are not so strict and write tests after doing the development.
Create a test
directory beneath calculus
, with an empty __init__.py
file. In a calculus/test/test_base_1.py
, put the
following:
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from calculus.base_1 import Calculation from twisted.trial import unittest class CalculationTestCase(unittest.TestCase): def test_add(self): calc = Calculation() result = calc.add(3, 8) self.assertEqual(result, 11) def test_subtract(self): calc = Calculation() result = calc.subtract(7, 3) self.assertEqual(result, 4) def test_multiply(self): calc = Calculation() result = calc.multiply(12, 5) self.assertEqual(result, 60) def test_divide(self): calc = Calculation() result = calc.divide(12, 5) self.assertEqual(result, 2)
You should now have the following 4 files:
calculus/__init__.py calculus/base_1.py calculus/test/__init__.py calculus/test/test_base_1.py
To run the tests, there are two things you must get set up. Make sure you get these both done - nothing below will work unless you do.
First, make sure that the directory that contains your
calculus
directory is in your Python load path. If you're
using the Bash shell on some form of unix (e.g., Linux, Mac OS X), run
PYTHONPATH="$PYTHONPATH:`pwd`/.."
at
the command line in the calculus
directory. Once you have your
Python path set up correctly, you should be able to run Python from the
command line and import calculus
without seeing
an import error.
Second, make sure you can run the trial
command. That is, make sure the directory containing the trial
program on you system is in your shell's PATH
. The easiest way to check if you have this is to
try running trial --help
at the command line. If
you see a list of invocation options, you're in business. If your shell
reports something like trial: command not found
,
make sure you have Twisted installed properly, and that the Twisted
bin
directory is in your PATH
. If
you don't know how to do this, get some local help, or figure it out by
searching online for information on setting and changing environment
variables for you operating system.
With those (one-time) preliminary steps out of the way, let's perform
the tests. Run trial calculus.test.test_base_1
from the
command line when you are in the directory containing the calculus
directory.
You should see the following output (though your files are probably not in
/tmp
:
$ trial calculus.test.test_base_1 calculus.test.test_base_1 CalculationTestCase test_add ... [FAIL] test_divide ... [FAIL] test_multiply ... [FAIL] test_subtract ... [FAIL] =============================================================================== [FAIL] Traceback (most recent call last): File "/tmp/calculus/test/test_base_1.py", line 8, in test_add self.assertEqual(result, 11) twisted.trial.unittest.FailTest: not equal: a = None b = 11 calculus.test.test_base_1.CalculationTestCase.test_add =============================================================================== [FAIL] Traceback (most recent call last): File "/tmp/calculus/test/test_base_1.py", line 23, in test_divide self.assertEqual(result, 2) twisted.trial.unittest.FailTest: not equal: a = None b = 2 calculus.test.test_base_1.CalculationTestCase.test_divide =============================================================================== [FAIL] Traceback (most recent call last): File "/tmp/calculus/test/test_base_1.py", line 18, in test_multiply self.assertEqual(result, 60) twisted.trial.unittest.FailTest: not equal: a = None b = 60 calculus.test.test_base_1.CalculationTestCase.test_multiply =============================================================================== [FAIL] Traceback (most recent call last): File "/tmp/calculus/test/test_base_1.py", line 13, in test_subtract self.assertEqual(result, 4) twisted.trial.unittest.FailTest: not equal: a = None b = 4 calculus.test.test_base_1.CalculationTestCase.test_subtract ------------------------------------------------------------------------------- Ran 4 tests in 0.042s FAILED (failures=4)
How to interpret this output? You get a list of the individual tests, each
followed by its result. By default, failures are printed at the end, but this
can be changed with the -e
(or --rterrors
) option.
One very useful thing in this output is the fully-qualified name of the
failed tests. This appears at the bottom of each =-delimited area of the
output. This allows you to copy and paste it to just run a single test you're
interested in. In our example, you could run trial
calculus.test.test_base_1.CalculationTestCase.test_subtract
from the
shell.
Note that trial can use different reporters to modify its output. Run
trial --help-reporters
to see a list of
reporters.
The tests can be run by trial
in multiple ways:
trial calculus
: run all the tests for the calculus package.trial calculus.test
: run using Python'simport
notation.trial calculus.test.test_base_1
: as above, for a specific test module. You can follow that logic by putting your class name and even a method name to only run those specific tests.trial --testmodule=calculus/base_1.py
: use thetest-case-name
comment in the first line ofcalculus/base_1.py
to find the tests.trial calculus/test
: run all the tests in the test directory (not recommended).trial calculus/test/test_base_1.py
: run a specific test file (not recommended).
You'll notice that Trial create a _trial_temp
directory in
the directory where you run the tests. This has a file called
test.log
which contains the log output of the tests (created
using log.msg
or log.err
functions). Examine this file if you add
logging to your tests.
Making the tests pass
Now that we have a working test framework in place, and our tests are
failing (as expected) we can go and try to implement the correct API. We'll do
that in a new version of the above base_1
module, calculus/base_2.py
:
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# -*- test-case-name: calculus.test.test_base_2 -*- class Calculation(object): def add(self, a, b): return a + b def subtract(self, a, b): return a - b def multiply(self, a, b): return a * b def divide(self, a, b): return a / b
We'll also create a new version of test_base_1 which imports and tests this
new implementation,
in calculus/test_base_2.py
:
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from calculus.base_2 import Calculation from twisted.trial import unittest class CalculationTestCase(unittest.TestCase): def test_add(self): calc = Calculation() result = calc.add(3, 8) self.assertEqual(result, 11) def test_subtract(self): calc = Calculation() result = calc.subtract(7, 3) self.assertEqual(result, 4) def test_multiply(self): calc = Calculation() result = calc.multiply(12, 5) self.assertEqual(result, 60) def test_divide(self): calc = Calculation() result = calc.divide(12, 5) self.assertEqual(result, 2)
trial
again as above, and your tests should now pass:
$ trial calculus.test.test_base_2 Running 4 tests. calculus.test.test_base CalculationTestCase test_add ... [OK] test_divide ... [OK] test_multiply ... [OK] test_subtract ... [OK] ------------------------------------------------------------------------------- Ran 4 tests in 0.067s PASSED (successes=4)
Factoring out common test logic
You'll notice that our test file contains redundant code. Let's get rid
of that. Python's unit testing framework allows your test class to define a
setUp
method that is called before
each test method in the class. This allows you to add attributes
to self
that can be used in tests
methods. We'll also add a parameterized test method to further simplify the
code.
Note that a test class may also provide the counterpart of setUp
, named tearDown
,
which will be called after each test (whether successful or
not). tearDown
is mainly used for post-test
cleanup purposes. We will not use tearDown
until later.
Create calculus/test/test_base_2b.py
as
follows:
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from calculus.base_2 import Calculation from twisted.trial import unittest class CalculationTestCase(unittest.TestCase): def setUp(self): self.calc = Calculation() def _test(self, operation, a, b, expected): result = operation(a, b) self.assertEqual(result, expected) def test_add(self): self._test(self.calc.add, 3, 8, 11) def test_subtract(self): self._test(self.calc.subtract, 7, 3, 4) def test_multiply(self): self._test(self.calc.multiply, 6, 9, 54) def test_divide(self): self._test(self.calc.divide, 12, 5, 2)
Much cleaner, no?
We'll now add some additional error tests. Testing just for successful
use of the API is generally not enough, especially if you expect your code
to be used by others. Let's make sure the Calculation
class raises exceptions if someone tries
to call its methods with arguments that cannot be converted to
integers.
We arrive at calculus/test/test_base_3.py
:
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from calculus.base_3 import Calculation from twisted.trial import unittest class CalculationTestCase(unittest.TestCase): def setUp(self): self.calc = Calculation() def _test(self, operation, a, b, expected): result = operation(a, b) self.assertEqual(result, expected) def _test_error(self, operation): self.assertRaises(TypeError, operation, "foo", 2) self.assertRaises(TypeError, operation, "bar", "egg") self.assertRaises(TypeError, operation, [3], [8, 2]) self.assertRaises(TypeError, operation, {"e": 3}, {"r": "t"}) def test_add(self): self._test(self.calc.add, 3, 8, 11) def test_subtract(self): self._test(self.calc.subtract, 7, 3, 4) def test_multiply(self): self._test(self.calc.multiply, 6, 9, 54) def test_divide(self): self._test(self.calc.divide, 12, 5, 2) def test_errorAdd(self): self._test_error(self.calc.add) def test_errorSubtract(self): self._test_error(self.calc.subtract) def test_errorMultiply(self): self._test_error(self.calc.multiply) def test_errorDivide(self): self._test_error(self.calc.divide)
We've added four new tests and one general-purpose function, _test_error
. This function uses the assertRaises
method, which takes an exception class,
a function to run and its arguments, and checks that calling the function
on the arguments does indeed raise the given exception.
If you run the above, you'll see that not all tests fail. In Python it's
often valid to add and multiply objects of different and even differing
types, so the code in the add and mutiply tests does not raise an exception
and those tests therefore fail. So let's add explicit type conversion to
our API class. This brings us to calculus/base_3.py
:
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# -*- test-case-name: calculus.test.test_base_3 -*- class Calculation(object): def _make_ints(self, *args): try: return map(int, args) except ValueError: raise TypeError("Couldn't coerce arguments to integers: %s" % args) def add(self, a, b): a, b = self._make_ints(a, b) return a + b def subtract(self, a, b): a, b = self._make_ints(a, b) return a - b def multiply(self, a, b): a, b = self._make_ints(a, b) return a * b def divide(self, a, b): a, b = self._make_ints(a, b) return a / b
Here the _make_ints
helper function tries to
convert a list into a list of equivalent integers, and raises a TypeError
in case the conversion goes wrong.
int
conversion can also
raise a TypeError
if passed something of the
wrong type, such as a list. We'll just let that exception go by as TypeError
is already what we want in case something
goes wrong.Twisted specific testing
Up to this point we've been doing fairly standard Python unit testing.
With only a few cosmetic changes (most importantly, directly importing
unittest
instead of using Twisted's unittest
version) we could make the
above tests run using Python's standard library unit testing framework.
Here we will assume a basic familiarity with Twisted's network I/O, timing, and Deferred APIs. If you haven't already read them, you should read the documentation on Writing Servers, Writing Clients, and Deferreds.
Now we'll get to the real point of this tutorial and take advantage of Trial to test Twisted code.
Testing a protocol
We'll now create a custom protocol to invoke our class from within a telnet-like session. We'll remotely call commands with arguments and read back the response. The goal will be to test our network code without creating sockets.
Creating and testing the server
First we'll write the tests, and then explain what they do. The first version of the remote test code is:
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from calculus.remote_1 import RemoteCalculationFactory from twisted.trial import unittest from twisted.test import proto_helpers class RemoteCalculationTestCase(unittest.TestCase): def setUp(self): factory = RemoteCalculationFactory() self.proto = factory.buildProtocol(('127.0.0.1', 0)) self.tr = proto_helpers.StringTransport() self.proto.makeConnection(self.tr) def _test(self, operation, a, b, expected): self.proto.dataReceived('%s %d %d\r\n' % (operation, a, b)) self.assertEqual(int(self.tr.value()), expected) def test_add(self): return self._test('add', 7, 6, 13) def test_subtract(self): return self._test('subtract', 82, 78, 4) def test_multiply(self): return self._test('multiply', 2, 8, 16) def test_divide(self): return self._test('divide', 14, 3, 4)
To fully understand this client, it helps a lot to be comfortable with the Factory/Protocol/Transport pattern used in Twisted.
We first create a protocol factory object. Note that we have yet to see
the RemoteCalculationFactory
class. It is in
calculus/remote_1.py
below. We
call buildProtocol
to ask the factory to build us a
protocol object that knows how to talk to our server. We then make a fake
network transport, an instance of twisted.test.proto_helpers.StringTransport
class (note that test packages are generally not part of Twisted's public API;
twisted.test.proto_helpers
is an exception). This fake
transport is the key to the communications. It is used to emulate a network
connection without a network. The address and port passed to buildProtocol
are typically used by the factory to choose to immediately deny remote connections; since we're using a fake transport, we can choose any value that will be acceptable to the factory. In this case the factory just ignores the address, so we don't need to pick anything in particular.
Testing protocols without the use of real network connections is both simple and recommended when testing Twisted code. Even though there are many tests in Twisted that use the network, most good tests don't. The problem with unit tests and networking is that networks aren't reliable. We cannot know that they will exhibit reasonable behavior all the time. This creates intermittent test failures due to network vagaries. Right now we're trying to test our Twisted code, not network reliability. By setting up and using a fake transport, we can write 100% reliable tests. We can also test network failures in a deterministic manner, another important part of your complete test suite.
The final key to understanding this client code is the _test
method. The call to dataReceived
simulates data arriving on the network
transport. But where does it arrive? It's handed to the lineReceived
method of the protocol instance (in
calculus/remote_1.py
below). So the client
is essentially tricking the server into thinking it has received the
operation and the arguments over the network. The server (once again, see
below) hands the work off to its CalculationProxy
object which in turn hands it to its
Calculation
instance. The result is written
back via sendLine
(into the fake string
transport object), and is then immediately available to the client, who
fetches it with tr.value()
and checks that it
has the expected value. So there's quite a lot going on behind the scenes
in the two-line _test
method above.
Finally, let's see the implementation of this protocol. Put the
following into calculus/remote_1.py
:
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# -*- test-case-name: calculus.test.test_remote_1 -*- from twisted.protocols import basic from twisted.internet import protocol from calculus.base_3 import Calculation class CalculationProxy(object): def __init__(self): self.calc = Calculation() for m in ['add', 'subtract', 'multiply', 'divide']: setattr(self, 'remote_%s' % m, getattr(self.calc, m)) class RemoteCalculationProtocol(basic.LineReceiver): def __init__(self): self.proxy = CalculationProxy() def lineReceived(self, line): op, a, b = line.split() a = int(a) b = int(b) op = getattr(self.proxy, 'remote_%s' % (op,)) result = op(a, b) self.sendLine(str(result)) class RemoteCalculationFactory(protocol.Factory): protocol = RemoteCalculationProtocol def main(): from twisted.internet import reactor from twisted.python import log import sys log.startLogging(sys.stdout) reactor.listenTCP(0, RemoteCalculationFactory()) reactor.run() if __name__ == "__main__": main()
As mentioned, this server creates a protocol that inherits from basic.LineReceiver
, and then a
factory that uses it as protocol. The only trick is the CalculationProxy
object, which calls Calculation
methods through remote_*
methods. This pattern is used frequently in
Twisted, because it is very explicit about what methods you are making
accessible.
If you run this test (trial
calculus.test.test_remote_1
), everything should be fine. You can also
run a server to test it with a telnet client. To do that, call python calculus/remote_1.py
. You should have the following output:
2008-04-25 10:53:27+0200 [-] Log opened. 2008-04-25 10:53:27+0200 [-] __main__.RemoteCalculationFactory starting on 46194 2008-04-25 10:53:27+0200 [-] Starting factory <__main__.RemoteCalculationFactory instance at 0x846a0cc>
46194 is replaced by a random port. You can then call telnet on it:
$ telnet localhost 46194 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. add 4123 9423 13546
It works!
Creating and testing the client
Of course, what we build is not particulary useful for now : we'll now build a client to our server, to be able to use it inside a Python program. And it will serve our next purpose.
Create calculus/test/test_client_1.py
:
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from calculus.client_1 import RemoteCalculationClient from twisted.trial import unittest from twisted.test import proto_helpers class ClientCalculationTestCase(unittest.TestCase): def setUp(self): self.tr = proto_helpers.StringTransport() self.proto = RemoteCalculationClient() self.proto.makeConnection(self.tr) def _test(self, operation, a, b, expected): d = getattr(self.proto, operation)(a, b) self.assertEqual(self.tr.value(), '%s %d %d\r\n' % (operation, a, b)) self.tr.clear() d.addCallback(self.assertEqual, expected) self.proto.dataReceived("%d\r\n" % (expected,)) return d def test_add(self): return self._test('add', 7, 6, 13) def test_subtract(self): return self._test('subtract', 82, 78, 4) def test_multiply(self): return self._test('multiply', 2, 8, 16) def test_divide(self): return self._test('divide', 14, 3, 4)
It's really symmetric to the server test cases. The only tricky part is that we don't use a client factory. We're lazy, and it's not very useful in the client part, so we instantiate the protocol directly.
Incidentally, we have introduced a very important concept here: the tests now return a Deferred object, and the assertion is done in a callback. When a test returns a Deferred, the reactor is run until the Deferred fires and its callbacks run. The important thing to do here is to not forget to return the Deferred. If you do, your tests will pass even if nothing is asserted. That's also why it's important to make tests fail first: if your tests pass whereas you know they shouldn't, there is a problem in your tests.
We'll now add the remote client class to produce calculus/client_1.py
:
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# -*- test-case-name: calculus.test.test_client_1 -*- from twisted.protocols import basic from twisted.internet import defer class RemoteCalculationClient(basic.LineReceiver): def __init__(self): self.results = [] def lineReceived(self, line): d = self.results.pop(0) d.callback(int(line)) def _sendOperation(self, op, a, b): d = defer.Deferred() self.results.append(d) line = "%s %d %d" % (op, a, b) self.sendLine(line) return d def add(self, a, b): return self._sendOperation("add", a, b) def subtract(self, a, b): return self._sendOperation("subtract", a, b) def multiply(self, a, b): return self._sendOperation("multiply", a, b) def divide(self, a, b): return self._sendOperation("divide", a, b)
More good practices
Testing scheduling
When testing code that involves the passage of time, waiting e.g. for a two hour timeout to occur in a test is not very realistic. Twisted provides a solution to this, the Clock
class that allows one to simulate the passage of time.
As an example we'll test the code for client request timeout: since our client uses TCP it can hang for a long time (firewall, connectivity problems, etc...). So generally we need to implement timeouts on the client side. Basically it's just that we send a request, don't receive a response and expect a timeout error to be triggered after a certain duration.
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from calculus.client_2 import RemoteCalculationClient, ClientTimeoutError from twisted.internet import task from twisted.trial import unittest from twisted.test import proto_helpers class ClientCalculationTestCase(unittest.TestCase): def setUp(self): self.tr = proto_helpers.StringTransportWithDisconnection() self.clock = task.Clock() self.proto = RemoteCalculationClient() self.tr.protocol = self.proto self.proto.callLater = self.clock.callLater self.proto.makeConnection(self.tr) def _test(self, operation, a, b, expected): d = getattr(self.proto, operation)(a, b) self.assertEqual(self.tr.value(), '%s %d %d\r\n' % (operation, a, b)) self.tr.clear() d.addCallback(self.assertEqual, expected) self.proto.dataReceived("%d\r\n" % (expected,)) return d def test_add(self): return self._test('add', 7, 6, 13) def test_subtract(self): return self._test('subtract', 82, 78, 4) def test_multiply(self): return self._test('multiply', 2, 8, 16) def test_divide(self): return self._test('divide', 14, 3, 4) def test_timeout(self): d = self.proto.add(9, 4) self.assertEqual(self.tr.value(), 'add 9 4\r\n') self.clock.advance(self.proto.timeOut) return self.assertFailure(d, ClientTimeoutError)
What happens here? We instantiate our protocol as usual, the only trick
is to create the clock, and assign proto.callLater
to
clock.callLater
. Thus, every callLater calls in the protocol
will finish before clock.advance()
returns.
In the new test (test_timeout), we call clock.advance
, that simulates and advance in time
(logically it's similar to a time.sleep
call). And
we just have to verify that our Deferred got a timeout error.
Let's implement that in our code.
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# -*- test-case-name: calculus.test.test_client_2 -*- from twisted.protocols import basic from twisted.internet import defer, reactor class ClientTimeoutError(Exception): pass class RemoteCalculationClient(basic.LineReceiver): callLater = reactor.callLater timeOut = 60 def __init__(self): self.results = [] def lineReceived(self, line): d, callID = self.results.pop(0) callID.cancel() d.callback(int(line)) def _cancel(self, d): d.errback(ClientTimeoutError()) def _sendOperation(self, op, a, b): d = defer.Deferred() callID = self.callLater(self.timeOut, self._cancel, d) self.results.append((d, callID)) line = "%s %d %d" % (op, a, b) self.sendLine(line) return d def add(self, a, b): return self._sendOperation("add", a, b) def subtract(self, a, b): return self._sendOperation("subtract", a, b) def multiply(self, a, b): return self._sendOperation("multiply", a, b) def divide(self, a, b): return self._sendOperation("divide", a, b)
The only important thing here is to not forget to cancel our callLater when everything went fine.
Cleaning up after tests
This chapter is mainly intended for people that want to have sockets or processes created in their tests. If it's still not obvious, you must try to avoid that like the plague, because it ends up with a lot of problems, one of them being intermittent failures. And intermittent failures are the plague of automated tests.
To actually test that, we'll launch a server with our protocol.
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from calculus.remote_1 import RemoteCalculationFactory from calculus.client_2 import RemoteCalculationClient from twisted.trial import unittest from twisted.internet import reactor, protocol class RemoteRunCalculationTestCase(unittest.TestCase): def setUp(self): factory = RemoteCalculationFactory() self.port = reactor.listenTCP(0, factory, interface="127.0.0.1") self.client = None def tearDown(self): if self.client is not None: self.client.transport.loseConnection() return self.port.stopListening() def _test(self, op, a, b, expected): creator = protocol.ClientCreator(reactor, RemoteCalculationClient) def cb(client): self.client = client return getattr(self.client, op)(a, b ).addCallback(self.assertEqual, expected) return creator.connectTCP('127.0.0.1', self.port.getHost().port ).addCallback(cb) def test_add(self): return self._test("add", 5, 9, 14) def test_subtract(self): return self._test("subtract", 47, 13, 34) def test_multiply(self): return self._test("multiply", 7, 3, 21) def test_divide(self): return self._test("divide", 84, 10, 8)
Recent versions of trial will fail loudly if you remove the
stopListening
call, which is good.
Also, you should be aware that tearDown
will
called in any case, after success or failure. So don't expect that every
objects you created in the test method are present, because your tests may
have failed in the middle.
Trial also has a addCleanup
method, which makes
these kind of cleanups easy and removes the need for tearDown
. For example, you could remove the code in _test
this way:
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def setUp(self): factory = RemoteCalculationFactory() self.port = reactor.listenTCP(0, factory, interface="127.0.0.1") self.addCleanup(self.port.stopListening) def _test(self, op, a, b, expected): creator = protocol.ClientCreator(reactor, RemoteCalculationClient) def cb(client): self.addCleanup(self.client.transport.loseConnection) return getattr(client, op)(a, b).addCallback(self.assertEqual, expected) return creator.connectTCP('127.0.0.1', self.port.getHost().port).addCallback(cb)
This remove the need of a tearDown method, and you don't have to check for the value of self.client: you only call addCleanup when the client is created.
Handling logged errors
Currently, if you send an invalid command or invalid arguments to our server, it logs an exception and closes the connection. This is a perfectly valid behavior, but for the sake of this tutorial, we want to return an error to the user if he sends invalid operators, and log any errors on server side. So we'll want a test like this:
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def test_invalidParameters(self): self.proto.dataReceived('add foo bar\r\n') self.assertEqual(self.tr.value(), "error\r\n")
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# -*- test-case-name: calculus.test.test_remote_1 -*- from twisted.protocols import basic from twisted.internet import protocol from twisted.python import log from calculus.base_3 import Calculation class CalculationProxy(object): def __init__(self): self.calc = Calculation() for m in ['add', 'subtract', 'multiply', 'divide']: setattr(self, 'remote_%s' % m, getattr(self.calc, m)) class RemoteCalculationProtocol(basic.LineReceiver): def __init__(self): self.proxy = CalculationProxy() def lineReceived(self, line): op, a, b = line.split() op = getattr(self.proxy, 'remote_%s' % (op,)) try: result = op(a, b) except TypeError: log.err() self.sendLine("error") else: self.sendLine(str(result)) class RemoteCalculationFactory(protocol.Factory): protocol = RemoteCalculationProtocol def main(): from twisted.internet import reactor from twisted.python import log import sys log.startLogging(sys.stdout) reactor.listenTCP(0, RemoteCalculationFactory()) reactor.run() if __name__ == "__main__": main()
If you try something like that, it will not work. Here is the output you should have:
trial calculus.test.test_remote_3.RemoteCalculationTestCase.test_invalidParameters calculus.test.test_remote_3 RemoteCalculationTestCase test_invalidParameters ... [ERROR] =============================================================================== [ERROR]: calculus.test.test_remote_3.RemoteCalculationTestCase.test_invalidParameters Traceback (most recent call last): File "/tmp/calculus/remote_2.py", line 27, in lineReceived result = op(a, b) File "/tmp/calculus/base_3.py", line 11, in add a, b = self._make_ints(a, b) File "/tmp/calculus/base_3.py", line 8, in _make_ints raise TypeError exceptions.TypeError: ------------------------------------------------------------------------------- Ran 1 tests in 0.004s FAILED (errors=1)
At first, you could think there is a problem, because you catch this
exception. But in fact trial doesn't let you do that without controlling it:
you must expect logged errors and clean them. To do that, you have to use the
flushLoggedErrors
method. You call it with the
exception you expect, and it returns the list of exceptions logged since the
start of the test. Generally, you'll want to check that this list has the
expected length, or possibly that each exception has an expected message. We do
the former in our test:
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from calculus.remote_2 import RemoteCalculationFactory from twisted.trial import unittest from twisted.test import proto_helpers class RemoteCalculationTestCase(unittest.TestCase): def setUp(self): factory = RemoteCalculationFactory() self.proto = factory.buildProtocol(('127.0.0.1', 0)) self.tr = proto_helpers.StringTransport() self.proto.makeConnection(self.tr) def _test(self, operation, a, b, expected): self.proto.dataReceived('%s %d %d\r\n' % (operation, a, b)) self.assertEqual(int(self.tr.value()), expected) def test_add(self): return self._test('add', 7, 6, 13) def test_subtract(self): return self._test('subtract', 82, 78, 4) def test_multiply(self): return self._test('multiply', 2, 8, 16) def test_divide(self): return self._test('divide', 14, 3, 4) def test_invalidParameters(self): self.proto.dataReceived('add foo bar\r\n') self.assertEqual(self.tr.value(), "error\r\n") errors = self.flushLoggedErrors(TypeError) self.assertEqual(len(errors), 1)
Resolve a bug
A bug was left over during the development of the timeout (probably several bugs, but that's not the point), concerning the reuse of the protocol when you got a timeout: the connection is not dropped, so you can get timeout forever. Generally an user will come to you saying "I have this strange problem on my crappy network environment. It seems you could solve it with doing XXX at YYY."
Actually, this bug can be corrected several ways. But if you correct it without adding tests, one day you'll face a big problem: regression. So the first step is adding a failing test.
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from calculus.client_3 import RemoteCalculationClient, ClientTimeoutError from twisted.internet import task from twisted.trial import unittest from twisted.test import proto_helpers class ClientCalculationTestCase(unittest.TestCase): def setUp(self): self.tr = proto_helpers.StringTransportWithDisconnection() self.clock = task.Clock() self.proto = RemoteCalculationClient() self.tr.protocol = self.proto self.proto.callLater = self.clock.callLater self.proto.makeConnection(self.tr) def _test(self, operation, a, b, expected): d = getattr(self.proto, operation)(a, b) self.assertEqual(self.tr.value(), '%s %d %d\r\n' % (operation, a, b)) self.tr.clear() d.addCallback(self.assertEqual, expected) self.proto.dataReceived("%d\r\n" % (expected,)) return d def test_add(self): return self._test('add', 7, 6, 13) def test_subtract(self): return self._test('subtract', 82, 78, 4) def test_multiply(self): return self._test('multiply', 2, 8, 16) def test_divide(self): return self._test('divide', 14, 3, 4) def test_timeout(self): d = self.proto.add(9, 4) self.assertEqual(self.tr.value(), 'add 9 4\r\n') self.clock.advance(self.proto.timeOut) return self.assertFailure(d, ClientTimeoutError) def test_timeoutConnectionLost(self): called = [] def lost(arg): called.append(True) self.proto.connectionLost = lost d = self.proto.add(9, 4) self.assertEqual(self.tr.value(), 'add 9 4\r\n') self.clock.advance(self.proto.timeOut) def check(ignore): self.assertEqual(called, [True]) return self.assertFailure(d, ClientTimeoutError).addCallback(check)
What have we done here ?
- We switched to StringTransportWithDisconnection. This transport manages
loseConnection
and forwards it to its protocol. - We assign the protocol to the transport via the
protocol
attribute. - We check that after a timeout our connection has closed.
For doing that, we then use the TimeoutMixin
class, that does almost everything we want. The great thing is that it almost
changes nothing to our class.
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# -*- test-case-name: calculus.test.test_client -*- from twisted.protocols import basic, policies from twisted.internet import defer class ClientTimeoutError(Exception): pass class RemoteCalculationClient(object, basic.LineReceiver, policies.TimeoutMixin): def __init__(self): self.results = [] self._timeOut = 60 def lineReceived(self, line): self.setTimeout(None) d = self.results.pop(0) d.callback(int(line)) def timeoutConnection(self): for d in self.results: d.errback(ClientTimeoutError()) self.transport.loseConnection() def _sendOperation(self, op, a, b): d = defer.Deferred() self.results.append(d) line = "%s %d %d" % (op, a, b) self.sendLine(line) self.setTimeout(self._timeOut) return d def add(self, a, b): return self._sendOperation("add", a, b) def subtract(self, a, b): return self._sendOperation("subtract", a, b) def multiply(self, a, b): return self._sendOperation("multiply", a, b) def divide(self, a, b): return self._sendOperation("divide", a, b)
Testing Deferreds without the reactor
Above we learned about returning Deferreds from test methods in order to make
assertions about their results, or side-effects that only happen after they
fire. This can be useful, but we don't actually need the feature in this
example. Because we were careful to use Clock
, we
don't need the global reactor to run in our tests. Instead of returning the
Deferred with a callback attached to it which performs the necessary assertions,
we can use a testing helper,
successResultOf
(and
the corresponding error-case helper
failureResultOf
), to
extract its result and make assertions against it directly. Compared to
returning a Deferred, this avoids the problem of forgetting to return the
Deferred, improves the stack trace reported when the assertion fails, and avoids
the complexity of using global reactor (which, for example, may then require
cleanup).
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from calculus.client_3 import RemoteCalculationClient, ClientTimeoutError from twisted.internet import task from twisted.trial import unittest from twisted.test import proto_helpers class ClientCalculationTestCase(unittest.TestCase): def setUp(self): self.tr = proto_helpers.StringTransportWithDisconnection() self.clock = task.Clock() self.proto = RemoteCalculationClient() self.tr.protocol = self.proto self.proto.callLater = self.clock.callLater self.proto.makeConnection(self.tr) def _test(self, operation, a, b, expected): d = getattr(self.proto, operation)(a, b) self.assertEqual(self.tr.value(), '%s %d %d\r\n' % (operation, a, b)) self.tr.clear() self.proto.dataReceived("%d\r\n" % (expected,)) self.assertEqual(expected, self.successResultOf(d)) def test_add(self): self._test('add', 7, 6, 13) def test_subtract(self): self._test('subtract', 82, 78, 4) def test_multiply(self): self._test('multiply', 2, 8, 16) def test_divide(self): self._test('divide', 14, 3, 4) def test_timeout(self): d = self.proto.add(9, 4) self.assertEqual(self.tr.value(), 'add 9 4\r\n') self.clock.advance(self.proto.timeOut) self.failureResultOf(d).trap(ClientTimeoutError) def test_timeoutConnectionLost(self): called = [] def lost(arg): called.append(True) self.proto.connectionLost = lost d = self.proto.add(9, 4) self.assertEqual(self.tr.value(), 'add 9 4\r\n') self.clock.advance(self.proto.timeOut) def check(ignore): self.assertEqual(called, [True]) self.failureResultOf(d).trap(ClientTimeoutError) self.assertEqual(called, [True])
This version of the code makes the same assertions, but no longer returns any
Deferreds from any test methods. Instead of making assertions about the result
of the Deferred in a callback, it makes the assertions as soon as
it knows the Deferred is supposed to have a result (in
the _test
method and in test_timeout
and test_timeoutConnectionLost
). The possibility
of knowing exactly when a Deferred is supposed to have a test is what
makes successResultOf
useful in unit testing, but prevents it from being
applicable to non-testing purposes.
successResultOf
will raise an exception (failing the test) if
the Deferred
passed to it does not have a result, or has a failure
result. Similarly, failureResultOf
will raise an exception (also
failing the test) if the Deferred
passed to it does not have a
result, or has a success result. There is a third helper method for testing the
final case,
assertNoResult
,
which only raises an exception (failing the test) if the Deferred
passed
to it has a result (either success or failure).
Dropping into a debugger
In the course of writing and running your tests, it is often helpful to
employ the use of a debugger. This can be particularly helpful in tracking down
where the source of a troublesome bug is in your code. Python's standard library
includes a debugger in the form of the
pdb module.
Running your tests with pdb
is as simple as invoking
twisted with the --debug
option, which will start
pdb
at the beginning of the execution of your test
suite.
Trial also provides a --debugger
option which can
run your test suite using another debugger instead. To specify a debugger other
than pdb
, pass in the fully-qualified name of an
object that provides the same interface as pdb
.
Most third-party debuggers tend to implement an interface similar to
pdb
, or at least provide a wrapper object that
does. For example, invoking trial with the line
trial --debug --debugger pudb
will open the
PuDB debugger instead, provided
it is properly installed.
Code coverage
Code coverage is one of the aspects of software testing that shows how much your tests cross (cover) the code of your program. There are different kind of measures: path coverage, condition coverage, statement coverage... We'll only consider statement coverage here, whether a line has been executed or not.
Trial has an option to generate the statement coverage of your tests. This option is --coverage. It creates a coverage directory in _trial_temp, with a file .cover for every modules used during the tests. The ones interesting for us are calculus.base.cover and calculus.remote.cover. In front of each line is the number of times you went through during the tests, or the marker '>>>>>>' if the line was not covered. If you went through all the tutorial to this point, you should have complete coverage :).
Again, this is only another useful pointer, but it doesn't mean your code is perfect: your tests should consider every possibile input and output, to get full coverage (condition, path, etc.) as well .
Conclusion
So what did you learn in this document?
- How to use the trial command-line tool to run your tests
- How to use string transports to test individual clients and servers without creating sockets
- If you really want to create sockets, how to cleanly do it so that it doesn't have bad side effects
- And some small tips you can't live without.