Iterating over test data in unit tests

[Ben Finney]

Howdy all,

Summary: I'm looking for idioms in unit tests for factoring out
repetitive iteration over test data. I explain my current practice,
and why it's unsatisfactory.


When following test-driven development, writing tests and then coding
to satisfy them, I'll start with some of the simple tests for a class.

import unittest

import bowling # Module to be tested

class Test_Frame(unittest.TestCase):

def test_instantiate(self):
""" Frame instance should be created """
instance = bowling.Frame()
self.failUnless(instance)

class Test_Game(unittest.TestCase):

def test_instantiate(self):
""" Game instance should be created """
instance = bowling.Game()
self.failUnless(instance)

As I add tests for more interesting functionality, they become more
data dependent.

class Test_Game(unittest.TestCase):

# ...

def test_one_throw(self):
""" Single throw should result in expected score """
game = bowling.Game()
throw = 5
game.add_throw(throw)
self.failUnlessEqual(throw, game.get_score())

def test_three_throws(self):
""" Three throws should result in expected score """
game = bowling.Game()
throws = (5, 7, 4)
game.add_throw(throws[0])
game.add_throw(throws[1])
game.add_throw(throws[2])
self.failUnlessEqual(sum(throws), game.get_score())

This cries out, of course, for a test fixture to set up instances.

class Test_Game(unittest.TestCase):

def setUp(self):
""" Set up test fixtures """
self.game = bowling.Game()

def test_one_throw(self):
""" Single throw should result in expected score """
throw = 5
score = 5
self.game.add_throw(throw)
self.failUnlessEqual(score, game.get_score())

def test_three_throws(self):
""" Three throws should result in expected score """
throws = [5, 7, 4]
score = sum(throws)
for throw in throws:
game.add_throw(throw)
self.failUnlessEqual(score, game.get_score())

def test_strike(self):
""" Strike should add the following two throws """
throws = [10, 7, 4, 7]
score = 39
for throw in throws:
game.add_throw(throw)
self.failUnlessEqual(score, game.get_score())

So far, this is just following what I see to be common practice for
setting up *instances* to test.

But the repetition of the test *inputs* also cries out to me to be
refactored. I see less commonality in doing this.

My initial instinct is just to put it in the fixtures.

class Test_Game(unittest.TestCase):

def setUp(self):
""" Set up test fixtures """
self.game = bowling.Game()

self.game_data = {
'one': dict(score=5, throws=[5]),
'three': dict(score=17, throws=[5, 7, 5]),
'strike': dict(score=39, throws=[10, 7, 5, 7]),
}

def test_one_throw(self):
""" Single throw should result in expected score """
throws = self.game_data['one']['throws']
score = self.game_data['one']['score']
for throw in throws:
self.game.add_throw(throw)
self.failUnlessEqual(score, game.get_score())

def test_three_throws(self):
""" Three throws should result in expected score """
throws = self.game_data['three']['throws']
score = self.game_data['three']['score']
for throw in throws:
game.add_throw(throw)
self.failUnlessEqual(score, game.get_score())

def test_strike(self):
""" Strike should add the following two throws """
throws = self.game_data['strike']['throws']
score = self.game_data['strike']['score']
for throw in throws:
game.add_throw(throw)
self.failUnlessEqual(score, game.get_score())

But this now means that the test functions are almost identical,
except for choosing one data set or another. Maybe that means I need
to have a single test:

def test_score_throws(self):
""" Game score should be calculated from throws """
for dataset in self.game_data:
score = dataset['score']
for throw in dataset['throws']:
self.game.add_throw(throw)
self.failUnlessEqual(score, self.game.get_score())

Whoops, now I'm re-using a fixture instance. Maybe I need an instance
of the class for each test case.

def setUp(self):
""" Set up test fixtures """
self.game_data = {
'one': dict(score=5, throws=[5]),
'three': dict(score=17, throws=[5, 7, 5]),
'strike': dict(score=39, throws=[10, 7, 5, 7]),
}

self.game_params = {}
for key, dataset in self.game_data.items():
params = {}
instance = bowling.Game()
params['instance'] = instance
params['dataset'] = dataset
self.game_params[key] = params

def test_score_throws(self):
""" Game score should be calculated from throws """
for params in self.game_params.values():
score = params['dataset']['score']
instance = params['instance']
for throw in params['dataset']['throws']:
instance.add_throw(throw)
self.failUnlessEqual(score, instance.get_score())

Good, now the tests for different sets of throws are in a dictionary
that's easy to add to. Of course, now I need to actually know which
one is failing.

def test_score_throws(self):
""" Game score should be calculated from throws """
for key, params in self.game_params.items():
score = params['dataset']['score']
instance = params['instance']
for throw in params['dataset']['throws']:
instance.add_throw(throw)
self.failUnlessEqual(score, instance.get_score(),
msg="Score mismatch for set '%s'" % key
)

It works. It's rather confusing though, since the actual test --
iterate over the throws and check the score -- is in the midst of the
iteration over data sets.

Also, that's just *one* type of test I might need to do. Must I then
repeat all that iteration code for other tests I want to do on the
same data?

Maybe I need to factor out the iteration into a generic iteration
function, taking the actual test as a function object. That way, the
dataset iterator doesn't need to know about the test function, and
vice versa.

def iterate_test(self, test_func, test_params=None):
""" Iterate a test function for all the sets """
if not test_params:
test_params = self.game_params
for key, params in test_params.items():
dataset = params['dataset']
instance = params['instance']
test_func(key, dataset, instance)

def test_score_throws(self):
""" Game score should be calculated from throws """
def test_func(key, dataset, instance):
score = dataset['score']
for throw in dataset['throws']:
instance.add_throw(throw)
self.failUnlessEqual(score, instance.get_score())

self.iterate_test(test_func)

That's somewhat clearer; the test function actually focuses on what
it's testing. Those layers of indirection are annoying, but they allow
the data sets to grow without writing more code to handle them.


Testing a rules-based system involves lots of data sets, and each data
set represents a separate test case; but the code for each of those
test cases is mindlessly repetitive. Factoring them out seems like it
needs a lot of indirection, and seems to make each test harder to
read. Different *types* of tests would need multiple iterators, more
complex test parameter dicts, or some more indirection. Those all
sound ugly, but so does repetitively coding every test function
whenever some new data needs to be tested.

How should this be resolved?

 

[Scott David Daniels]

Summary: I'm looking for idioms in unit tests for factoring out
repetitive iteration over test data....

How about something like:

import unittest, bowling
class Test_Game(unittest.TestCase):
def setUp(self):
""" Set up test fixtures """
self.game = bowling.Game()

def runs(self, throws):
"""Run a series of scores and return the result"""
for throw in throws:
self.game.add_throw(throw)
return self.game.get_score()

def test_one_throw(self):
""" Single throw should result in expected score """

self.assertEqual(5, self.runs([5]))

def test_three_throws(self):
""" Three throws should result in expected score """

self.assertEqual(5 + 7 + 4, self.runs([5, 7, 4]))

def test_strike(self):
""" Strike should add the following two throws """

self.assertEqual(39, self.runs([10, 7, 4, 7]))


There is no reason you cannot write support functions.

 

[Ben Finney]

Summary: I'm looking for idioms in unit tests for factoring out
repetitive iteration over test data....

How about something like:

class Test_Game(unittest.TestCase):

[...]
def runs(self, throws):
"""Run a series of scores and return the result""" [...]

def test_one_throw(self):
""" Single throw should result in expected score """

self.assertEqual(5, self.runs([5]))

def test_three_throws(self):
""" Three throws should result in expected score """

self.assertEqual(5 + 7 + 4, self.runs([5, 7, 4]))

def test_strike(self):
""" Strike should add the following two throws """

self.assertEqual(39, self.runs([10, 7, 4, 7]))

Yes, I'm quite happy that I can factor out iteration *within* a single
data set. That leaves a whole lot of test cases identical except for
the data they use.

The question remains: how can I factor out iteration of *separate test
cases*, where the test cases are differentiated only by the data they
use? I know at least one way: I wrote about it in my (long) original
post. How else can I do it, with less ugliness?

 

[Bengt Richter]

Howdy all,

Summary: I'm looking for idioms in unit tests for factoring out
repetitive iteration over test data. I explain my current practice,
and why it's unsatisfactory.

Does this do what you want?
http://codespeak.net/py/current/doc/test.html#generative-tests-yielding-more-tests

Regards,
Bengt Richter

 

[Steven Bethard]

Maybe I need to factor out the iteration into a generic iteration
function, taking the actual test as a function object. That way, the
dataset iterator doesn't need to know about the test function, and
vice versa.

def iterate_test(self, test_func, test_params=None):
""" Iterate a test function for all the sets """
if not test_params:
test_params = self.game_params
for key, params in test_params.items():
dataset = params['dataset']
instance = params['instance']
test_func(key, dataset, instance)

def test_score_throws(self):
""" Game score should be calculated from throws """
def test_func(key, dataset, instance):
score = dataset['score']
for throw in dataset['throws']:
instance.add_throw(throw)
self.failUnlessEqual(score, instance.get_score())

self.iterate_test(test_func)

That's somewhat clearer; the test function actually focuses on what
it's testing. Those layers of indirection are annoying, but they allow
the data sets to grow without writing more code to handle them.

Don't know if this helps, but I'd be more likely to write this as
something like (untested)::

def get_tests(self, test_params=None):
""" Iterate a test function for all the sets """
if not test_params:
test_params = self.game_params
for key, params in test_params.items():
dataset = params['dataset']
instance = params['instance']
yield key, dataset, instance

def test_score_throws(self):
""" Game score should be calculated from throws """
for key, dataset, instance in self.get_tests()
score = dataset['score']
for throw in dataset['throws']:
instance.add_throw(throw)
self.failUnlessEqual(score, instance.get_score())

That is, make an interator to the various test information, and just put
your "test_func" code inside a for-loop.

STeVe

 

[Ben Finney]

Summary: I'm looking for idioms in unit tests for factoring out
repetitive iteration over test data.

Thanks to those who've offered suggestions, especially those who
suggested I look at generator functions. This leads to::

import unittest

import bowling # Module to be tested

class Test_Game(unittest.TestCase):
""" Test case for the Game class """

def setUp(self):
""" Set up test fixtures """
self.game_data = {
'none': dict(score=0, throws=[], frame=1),
'one': dict(score=5, throws=[5], frame=1),
'two': dict(score=9, throws=[5, 4], frame=2),
'three': dict(score=14, throws=[5, 4, 5], frame=2),
'strike': dict(score=26, throws=[10, 4, 5, 7], frame=3),
}

self.game_params = {}
for key, dataset in self.game_data.items():
params = {}
instance = bowling.Game()
params['instance'] = instance
params['dataset'] = dataset
self.game_params[key] = params

def iterate_params(test_params=None):
""" Yield the test parameters """
if not test_params:
test_params = self.game_params
for key, params in test_params.items():
dataset = params['dataset']
instance = params['instance']
yield key, dataset, instance

def test_score_throws(self):
""" Game score should be calculated from throws """
for key, dataset, instance in self.iterate_params():
score = dataset['score']
for throw in dataset['throws']:
instance.add_throw(throw)
self.failUnlessEqual(score, instance.get_score())

def test_current_frame(self):
""" Current frame should be as expected """
for key, dataset, instance in self.iterate_params():
frame = dataset['frame']
for throw in dataset['throws']:
instance.add_throw(throw)
self.failUnlessEqual(frame, instance.current_frame)

That's much better. Each test is now clearly about looping through the
datasets, but the infrastructure to do so is factored out. Adding a
test case modelled on the existing cases just means adding a new entry
to the game_data dictionary. Setting up a different kind of test --
e.g. for invalid game data -- just means setting up a new params
dictionary and feeding that to the same generator function.

I like it. Can it be improved? Are there readability problems that can
be fixed? Is the test fixture setup too complex? Should the iterator
become even more general, and be refactored out to a test framework
for the project?

 

[Scott David Daniels]

Thanks to those who've offered suggestions, especially those who
suggested I look at generator functions. This leads to::

Here's another way (each test should independently test one feature):

class Test_Game(unittest.TestCase):
""" Test case for the Game class """
score = 0
throws = []
frame = 1

def setUp(self):
""" Set up test fixtures """

self.game = bowling.Game()

def test_score_throws(self):
""" Game score should be calculated from throws """
for throw in self.throws:
self.game.add_throw(throw)
self.assertEqual(self.score, self.game.get_score())

def test_current_frame(self):
""" Current frame should be as expected """
frame = dataset['frame']
for throw in self.throws:
self.game.add_throw(throw)
self.assertEqual(self.frame, self.game.current_frame)

class Test_one(Test_Game):
score = 5
throws = [5]
frame = 1

class Test_two(Test_Game):
score = 9
throws = [5, 4]
frame = 2

class Test_three(Test_Game):
score = 14
throws = [5, 4, 5]
frame = 2

class Test_strike(Test_Game):
score = 26
throws = [10, 4, 5, 7]
frame = 3

--Scott David Daniels
(e-mail address removed)