CODEWITHSUNDEEP
python-3.xunit-testingtddnose
jchud13
jchud13

Reputation: 55

How do I unit test for failing tests?

I am trying to get started with nosetests and TDD on my own. From what I understand the point of unit testing is to test as much functionality of a function as possible. So what I want to do is add invalid parameters to my function and verify that this can not be done. For example, I am writing a simple add function

def addBowling(x, y):
    try:
        return x + y
    except TypeError:
        print('Exception occured: invalid types')

So for this function I want inputs like 'a' to raise an exception. In my nosetests I want to input 'a' like so. 

def testAddNumbers():
    assert addBowling(3, 4) == 7
    assert addBowling(5, 0) == 5
    assert addBowling('a', 0) == TypeError

I want to have a couple asserts that will pass and one assert that will fail. When I run this test it tells me that 1 test failed. I am not sure if I am correct in my understanding but I want this test to say it passed because this is correct functionality for my function.

Any guidance on how to get the results that I am looking for?

Upvotes: 1

Views: 31

Answers (1)

jchud13
jchud13

Reputation: 55

Thanks to a helpful commenter I was able to learn that assert raises is what I was looking for. I refactored my function so now all it does is add and used assert raises in my test, like so.

def addBowling(x, y):
        return x + y

def testAddNumbers():
    assert addBowling(3, 4) == 7
    assert addBowling(5, 0) == 5
    assert_raises(TypeError, addBowling, 'a', 2)

Don't forget to import from nose.tools assert_raises!

Upvotes: 1

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