How to unittest every class with the same public API in a module with python?

Question

I have a module which parses different file formats like CSV, XLS, HTML, etc.
The different formats contains exactly the same information, so I made different classes for parsing different file types. These classes have the exact same public API, and obviously have the same base class like this:

class BaseParser(object):
    def countTotalValues(self):
        pass

    def countItems(self):
        pass

class CSVParser(BaseParser):
    def __init__(self):
        """Init data, check for errors, etc.."""

    def parse(self):
        """ parses the data and set the result dictionaries like self.values, self.items, etc."""

class XLSParser(BaseParser):
    """ Ha exactly the same public API as CSVParser and set the same inner values. """
    pass

Is it a good idea to unit test each of the classes at once with the same values ? I have been doing this:

class TestParserClasses(unittest.TestCase):
    def setUp(self):
        self.instances = []
        for class_, file_ in PARSER_CLASSES:
            self.instances.append(class_(file_))

    def tearDown(self):
        del self.instances

and define every unit test this way:

    def test_count_total_values_without_parameter(self):
        for parser in self.instances:
            parser.parse()
            self.assertEqual(Decimal('9216.84'), parser.countTotalValues())

    def test_count_items_without_parameter(self):
        for parser in self.instances:
            parser.parse()
            self.assertEqual(128, parser.countItems())

Is it okay to do this? If yes, how to unit test all of them with the same TestCases at once without

    for parser in self.instances:
        parser.parse()

So I want to write unittest like this:

def test_count_total_values_without_parameter(self):
    self.assertEqual(Decimal('9216.84'), parser.countTotalValues())

def test_count_items_without_parameter(self):
    self.assertEqual(128, parser.countItems())

applied to every class. Is it possible ?

This seems more or less similar to stackoverflow.com/questions/16305985/unit-test-suite-in-python. To answer your question if you should test multiple implementations in one test, I'd say no, because this doesn't give you the info which of them failed and which didn't. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented May 16, 2013 at 15:41

Mattie B · Accepted Answer · 2013-05-16 15:51:03Z

1

Have you considered creating a base TestCase and subclassing it for each of the classes you wish to test?

Create it like this, containing your actual test methods, and keep it in a separate module that does not match the test module pattern (by default, test*.py) so unittest won't discover it:

import unittest

class BaseTestCase(unittest.TestCase):
    def test_count_total_values_without_parameter(self):
        self.assertEqual(Decimal('9216.84'), self.parser.countTotalValues())

    # …more tests…

Now, in your test modules, do something like this:

import basetest

class TestCSVParser(basetest.BaseTestCase):
    def setUp(self):
        self.parser = CSVParser()

class TestXLSParser(basetest.BaseTestCase):
    def setUp(self):
        self.parser = XLSParser()

edited May 16, 2013 at 15:51

answered May 16, 2013 at 15:31

Mattie B

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8 Comments

Ulrich Eckhardt Over a year ago

This will run three tests: BaseTestCase.test_count..., TestCSVParser.test_count... and TestXLSParser.test_count..., because BaseTestCase will be autodetected as testcase in and of itself. The simple remedy is to write a mixin class with the test_count_... function and use multiple inheritance from both unittest.TestCase and baseTestCase.

Mattie B Over a year ago

@UlrichEckhardt That was why I kept BaseTestCase in a separate module. I created a simpler version of this to verify before making my post and python -m unittest discover did not pick up the basetest module; only the child testcases in the test module were picked up, since it matches the test*.py glob (see docs.python.org/2/library/unittest.html#test-discovery)

kissgyorgy Over a year ago

With @UlrichEckhardt's suggestion, this is great !

kissgyorgy Over a year ago

I updated the answer with @UlrichEckhardt 's suggestion and will accept it if you approve my edit.

Mattie B Over a year ago

@Walkman Thank you, but I would suggest going ahead and writing up your own answer with your preferred solution and accepting it. There are definitely multiple ways to do this one.

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