Better Test Cases

Nov 10, 2011

The single most important thing you can do to help your code is not just to test, but to use a good test case. Bugs often sneak through a vague test case. For example, let’s say I want to test that when a new customer is created, the url for the customer is prefixed with the proper http protocol. I might write something like this:

def test_url_is_prefixed    customer = Customer.create!(:url => "")    assert customer.url == "" end

Assuming I have a before save filter, this test will pass. But it’s not a good test. It’s simple and to the point, but this test case needs another test. What happens if an empty string is sent? Then “http://” gets returned and the feature is broken, but the tests pass. Add another test case.

def test_url_is_not_prefixed_for_empty_string    customer = Customer.create!(:url => "")    assert customer.url == "" end

Now I have handled a more specific test case. I wanted to use the term scenario instead of test case, but that is synonymous with cucumber. Scenario is really a better term. When testing a method, I am usually testing a series of test cases, but I always keep mindful to keep my tests short. Always ask “What if…”

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