Modern, Pythonic unit testing¶
The Why¶
I’m not satisfied with the existing testing solutions.
- The standard unittest library is overly complicated and its API doesn’t make sense for the problem it tries to solve. Classes are great for inheritance and multiple instances but tests are merely collections of callbacks. The use of camel case mixes badly with the code I’m testing which always follows PEP 8.
- Nose has the right idea with the @istest decorator but as it’s not actually collecting marked tests it has to discover them all, which means you need a global namespace of tests if you’re going flat. Test discovery relies on naming conventions and doesn’t really adhere to the idiom that “explicit is better than implicit”. Setup and teardown of flat tests doesn’t ensure isolation.
- Admittedly I haven’t tried py.test, but when I look at it I just see a big mess of metaprogrammatic string-programming magic. Not my cup of tea.
In my mind, tests are:
- Applications. I want to write my tests like I write application code.
- Collections of callables that fail if they raise unhandled exceptions.
The Zen of Python applies to testing just as well as to any other code.
The How¶
Attest provides two styles for writing tests, one functional and one object-oriented. The functional API is inspired by that of Flask, not for bandwagony reasons, but because it’s a well-fit pattern for the problem of “collections of callables”. The object-oriented style follows standard Python idioms for writing classes. It’s easy to invent your own style because Attest only assumes that a test is a callable and a collection an iterable. There is no magic you have to account for - Attest is a library for writing tests rather than a scriptable program for running tests. It’s up to you to organize and collect tests, though Attest will assist you.
Assertions are done with operator overloading; while I’m not usually too fond of DSLs, I also find it difficult to remember all the unittest assertion methods. Using the actual operators help.
from attest import Tests, Assert
math = Tests()
@math.test
def arithmetics():
"""Ensure that the laws of physics are in check."""
Assert(1 + 1) == 2
math.run()
