Sunday 7 February 2010 — This is almost 15 years old. Be careful.
A minor hiccup in writing unit tests is how to name the classes that contain them. The jUnit style of test class, which has been adopted by virtually everyone, including Python’s unittest module, is that tests are methods of a class. The class is instantiated once for each test method, then three methods are called: setUp, the test method, and tearDown.
As a result, you end up with test classes that look like this:
# Tests for double_it, and no, no one would write them this way...
class DoubleItTests(unittest.TestCase):
def test_ten(self):
assert double_it(10) == 20
def test_twenty(self):
assert double_it(20) == 40
Here I’ve named the class DoubleItTests, plural. That’s because I can see that it’s a container for a number of tests. This feels right if you think about the class simply as a namespace for the test methods.
But what is instantiated from the class? Only single tests. In this case, the class will be instantiated twice, once to run test_ten, and once to run test_twenty. The class’ name should really be the name of the objects. No one would name their user class Users under the theory that the class encompasses a number of users.
So the test class should really be called DoubleItTest, which I guess fits in with the unittest.TestCase base class it derives from. But somehow it just looks wrong.
This is reminiscent of the SQL table naming dilemma. Is it the CUSTOMER table, or the CUSTOMERS table? How you feel about it seems to come down to whether you think natively in SQL, or whether it’s just a backing store for your ORM.
I’m getting used to the singular test class name, but it still doesn’t come naturally, I have to remind myself to leave off those tempting plurals.
Comments
Thanks for pointing out the blinders I've been wearing... I think...
As for naming entities in SQL? Relations aren't containers either. I try to make my databases relational, even where SQL's non-relational warts make that difficult; so all the relations are named in the singular.
class Test_DoubleIt(unittest.TestCase): def test_ten(self): assert double_it(10) == 20 def test_twenty(self): assert double_it(20) == 40All my test classes start with Test_, so I don't have to think about singular or plural. Moreover, it blends nicely with the test themselves starting with test_.class Users: def GetBob(): return Bob def GetJill(): return JillThen calling it plural would be correct. It really is just a container, just like the unit test container... even though you only use it for one test/user at a time.This is especially apt for the testcases, because programmers aren't ever going to actually instantiate the class themselves. You'll never see
testcase = DoubleItTests()
It's the nature of the JUnit style that it's all automated, and the classes really *are* just a namespace... so don't fight it, let it be plural... since most of the time you're talking about them, you're talking about them in the plural "hey - one of the DoubleItTests failed". "Can you add that as a new test to the DoubleItTests?" "Where's that test again? Oh right, in DoubleItTests".
Second, has it ever occurred to you that this naming problem might be a symptom of something deeper — namely, that it's a semantic confusion to wrap tests in a class in the first place, when they're not behaviors of a persistent object (which is what the "class" concept was invented to express in the first place)? Precisely this kind of semantic overhead is the reason that I encourage everyone to try out "nose" or "py.test", and simply write their test cases as functions, and see whether the semantics flatten out into something easier to manage. A test class might make sense if setUp() sets several instance variables that the tests then use to avoid creating a test database over and over again — in which case ExampleDatabaseTests becomes a reasonable thing to have a name for! But in other cases the class is just cognitive overhead. And given that "nose" and "py.test" have ways to have setUp and tearDown as simple functions, I'm not even sure whether a class is ever useful!
More commonly, I just use the TestCase subclasses as a way to organize the tests. For example, one class being tested typically gets one TestCase. A module under test gets one test script/module. This of course breaks down when testing functions or doing integration testing though.
At the test module level, I name things moduleundertest_test.py. Mostly because having a directory full of test scripts prefixed with the word "test" is really annoying when you want to run just one from the shell. But that's a different matter.
A nitpick I have with unittest is the spelling of setUp(). Even after using unittest for many many years, I'm constantly leaving the "U" lower-case, because it's one word damn it all! Even ignoring pep8 it's still wrong. Sometimes it's the littlest things than can slowly drive us crazy. 8^)
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