Fixing a poorly written Django website (no unit tests)

[Some Developer]

Hi,

I've been working on a Django website for about 2 months on and off and
am nearing the end of development work where I can start thinking about
making it look pretty and the after that deploy to production.

I've been doing lots of manual testing and I'm sure that the website
works correctly but due to the need to get the website in production
ASAP and my lack of unit testing experience with Django (I'm still not
entirely sure what the point of unit testing a 2 or 3 line Django view
is when you can clearly see if it is correct or not) I've neglected
automated testing.

While I'm still going to go ahead and launch the site in production as
soon as it is deployed I want to go back and add in all the unit tests
that are missing. How would you tackle this problem?

Most of the code is pretty simple but there are ecommerce elements that
I have tested extensively by running my code through the Python
debugger. These must always work.

I'm a bit ashamed that it has got this far but I'm mainly a C developer
and unit testing isn't pushed quite so hard there (even though it should
be).

Any help appreciated.

[Avraham Serour]

Manual testing takes time and are prone to errors because they are done by humans, automatic testing means that when changing something in the code you can just run the tests, you don't need to run the server, open the browser, click, click and see if something seems out of order, then open the js console to see if it throws any error, then add some console.log, then remove them and so on...

It is actually hard to understand why you would need testing for something small, but as with every project, you'll need to add features and the code will grow slowly with time, before you realize you already have something big

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[Dan Gentry]

No need to test the Django provided logic, but I like to write a few tests for each view that check the permissions, urls, updates, etc.  More of a functional test than a unit test.  I find that when these tests fail it is usually something changed somewhere else in the app.  For example, a change to a model that alters validation of an update.

In the case of your ecommerce code, complete tests can make your process of testing much faster compared to manual debugging work, plus they will test all areas of the code the same way every time.  Less chance for omission or error.  Confidence in the code goes up.

[Mike Dewhirst]

On 4/03/2015 11:01 PM, Some Developer wrote:
> Hi,
>
> I've been working on a Django website for about 2 months on and off and
> am nearing the end of development work where I can start thinking about
> making it look pretty and the after that deploy to production.
>
> I've been doing lots of manual testing and I'm sure that the website
> works correctly but due to the need to get the website in production
> ASAP and my lack of unit testing experience with Django (I'm still not
> entirely sure what the point of unit testing a 2 or 3 line Django view
> is when you can clearly see if it is correct or not) I've neglected
> automated testing.
>
> While I'm still going to go ahead and launch the site in production as
> soon as it is deployed I want to go back and add in all the unit tests
> that are missing. How would you tackle this problem?

Use Coverage. https://pypi.python.org/pypi/coverage/3.7.1

Best thing since sliced bread ...

[Ilya Kazakevich]

You may start from highest level testing: 

1) create "usage scenarios" for your website. Like "customer opens page 'foo', and should see 'bar'". You use such scenarios for manual testing, right?

2) code such scenarios against Django project. You may use BDD testing tools (like lettuce or behave), or do it in pure python. You may call Django views and templates directly (using django unittesting support or lettuce/harvest), or do it through the browser using Selenium. One scenario -- one method. Yes, there is a lot of boilerplate code, but you only need to write it once. BDD tools are used to simplify this process by writing scenarios on DSL called Gherkin, which is easier. 

This is some kind of "acceptance testing", the one that helps you to be sure website works like customer expects it to work. Every project should have one, I believe.

After it, you may find that some units of your system are complex and error prone. What is unit? Unit is module, function or even package with _clear interface_. You then create unit tests against this module. Only units with complex logic need to be tested. No need to test simple view that just returns render(): this view is tested as part of high level testing. But if you have function "calc_user_amount" and complex business logic stands behind it, you may create unit test for it.

There are 3 mistakes people do about testing:

1) Testing each function, even private function, even 1 line function. It takes a lot of time, and such tests are fragile. You throw'em away after simple refactoring.

2) Testing "in the middle of abstraction": I mean testing functions with out of clear interface, like private functions. If you need to read function code before writing test (pydoc is not enough), you should not test this function. Try a higher level of abstraction.

3) Skipping high level testing: even if all your code is covered with low-level unit-tests, you still need high level testing like the one with Selenium to make sure everything works correctly, and when you refactor your code you use such testing to make sure you did not break anything.

So, you start with high level, and then cover _some_ units with unit test, if you believe they may contain error.

[Carl Meyer]

This is really excellent advice.

Carl

[Some Developer]

Awesome advice. Thanks!

I bought a book called "Test Driven Development using Python" and have
had a look through it a bit. It does seem a bit over the top (write no
code until you have a unit test for it in existence even if it is just a
one liner view function) but hopefully I'll be able to take some of the
advice and use it to fix up my code base.

Has anyone else read the book? Any opinions?

[Kevin Ndung'u]

I have read the book and it got me started in Django when I knew absolutely nothing about testing.
Though it might be a bit over the top, it manages to teach you the concepts so that you can later on apply on them on your own.
I highly recommend it.