How do you generate dynamic (parameterized) unit tests in Python?

Question

I have some kind of test data and want to create a unit test for each item. My first idea was to do it like this:

import unittest  l = [["foo", "a", "a",], ["bar", "a", "b"], ["lee", "b", "b"]]  class TestSequence(unittest.TestCase):     def testsample(self):         for name, a,b in l:             print "test", name             self.assertEqual(a,b)  if __name__ == '__main__':     unittest.main() 

The downside of this is that it handles all data in one test. I would like to generate one test for each item on the fly. Any suggestions?

Answer 1

This is called "parametrization".

There are several tools that support this approach. E.g.:

• pytest's decorator
• parameterized

The resulting code looks like this:

from parameterized import parameterized  class TestSequence(unittest.TestCase):     @parameterized.expand([         ["foo", "a", "a",],         ["bar", "a", "b"],         ["lee", "b", "b"],     ])     def test_sequence(self, name, a, b):         self.assertEqual(a,b) 

Which will generate the tests:

test_sequence_0_foo (__main__.TestSequence) ... ok test_sequence_1_bar (__main__.TestSequence) ... FAIL test_sequence_2_lee (__main__.TestSequence) ... ok  ====================================================================== FAIL: test_sequence_1_bar (__main__.TestSequence) ---------------------------------------------------------------------- Traceback (most recent call last):   File "/usr/local/lib/python2.7/site-packages/parameterized/parameterized.py", line 233, in <lambda>     standalone_func = lambda *a: func(*(a + p.args), **p.kwargs)   File "x.py", line 12, in test_sequence     self.assertEqual(a,b) AssertionError: 'a' != 'b' 

For historical reasons I'll leave the original answer circa 2008):

I use something like this:

import unittest  l = [["foo", "a", "a",], ["bar", "a", "b"], ["lee", "b", "b"]]  class TestSequense(unittest.TestCase):     pass  def test_generator(a, b):     def test(self):         self.assertEqual(a,b)     return test  if __name__ == '__main__':     for t in l:         test_name = 'test_%s' % t[0]         test = test_generator(t[1], t[2])         setattr(TestSequense, test_name, test)     unittest.main()