A nano tutorial on Test Driven Development (TDD) and Continuous Integration (CI). Let's check if a number is prime or not.
TDD allows us to write software based on goals or tests. Pass all the tests and the software is done.
Bare minimum things we need to start is
- some hardcoded output*
- test cases we want the software (which you will write) to handle
*that looks like output. i.e., same data structure, same data-type, etc.,
It is okay to begin with a hardcoded value or random variable being outputted. And now when we run the tests, some will pass and some will fail. This should give an estimate of how much we have progressed. We then write code to make every test pass. Some test cases can be added along the way as well just like we did in this repo, if you do not know all the test cases before building the software.
Maybe. Maybe not. Depends on
- effort you would put in to write the tests
- time to test all those cases manually
- development iterations
- number of developers involved
If it's a single developer and a one iteration build (which even small projects usually won't be) that can be easily tested manually and if it would take ages to write them as code, yes you may not want to do this. You can write the software once and for all, see if it works at the end, make quick changes or add dirty hacks just to get it working, hand it over and done, right?
But unfortunately, even a very simple task like is_prime(number) would require multiple iterations. Every single time you make changes, you can check if the change you made has broken your app or not.
It would become so messy when more than one developer is involved. How do I know if I broke the code, or my colleague broke it? Run the tests before and after your colleague's commit, and voila! You know who the criminal is ;)
And remember, passing the tests do not mean your code is bug-free, it just means that it passes the test cases that we aimed for.
With CI, we can be sure if this piece of software will work just the way we would expect on any machine with a given configuration in the world. In this case, we ensure this software runs on any machine that can run
- Python 2.6
- Python 2.7
- Python 3.4
- Python 3.5
- Python 3.6
- Python 3.7-dev
You would want to use CI unless you are happy if it runs only on your machine (which has it's own environment variables and specific versions of dev-software installed) or have plenty of time to test your app on all different versions manually and you won't get bored at all ;)
That's an example of something as simple as is_prime() breaking for a few versions of python. Yes, expect for things to break when it leaves your computer. It happens so often and it's common :D
Check the commit history of this repo and that should help you get started.
Copyright (c) 2018 Saravanabalagi Ramachandran
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