Specification Tests¶

“If it’s not tested, it’s broken.” - Bruce Eckel.

Testing assure you that the code works... at least in one very specific case.

Why do we love unit tests?¶

We love unit tests because they...

help writing better code in the first place
make refactoring possible
keep internal API tidy
help design and document the intended behaviour of the code

Why do we hate unit tests?¶

We hate unit tests because they...

need as much work as code
need to be refactored during a refactoring
break when you change trivial implementation details
risk keeping the focus on the process, not on the product

Feature vs. implementation¶

How to test for a feature without knowing the implementation?¶

Examples¶

Another example, find a function that decomposes a URL into individual rfc3986 components:

$ py.test examples/test_rfc3986_parse.py --candidates-from-modules urllib.parse
[...]
examples/test_rfc3986_parse.py::test_rfc3986_parse_basic[urllib.parse:urlparse] HIT
examples/test_rfc3986_parse.py::test_rfc3986_parse_basic[urllib.parse:urlsplit] HIT
[...]

the two functions urlparse and urlsplit pass the basic rfc3986 parsing test, but do not pass the more complex test_rfc3986_parse_full test.

More advanced functions are available on PyPI:

$ pip install urllib3
$ py.test examples/test_rfc3986_parse.py --candidates-from-modules urllib3
[...]
examples/test_rfc3986_parse.py::test_rfc3986_parse_basic[urllib3.util.url:parse_url] HIT
examples/test_rfc3986_parse.py::test_rfc3986_parse_full[urllib3.util.url:parse_url] HIT
[...]

now the function parse_url in the module urllib3.util.url passes both tests.