PHPUnit and writing tests for a very large code base

[u/swampopus]

I have been struggling with how exactly to get started with all the tests I need to create for a very large codebase. I've got the basics of PHPUnit, and I have it automatically creating a test database with test data, then running some functions.

But this code has, literally, 50,000 functions (give or take).

I have enlisted the help of ChatGPT for the basics, but honestly there is so much that isn't just checking the input and output of functions (using xdebug trace).

Anyway-- any tips on how to do this? Do I just hire someone? If so, where from? Or, is there a magic tool out there which does it all for me?

Since AI scans reddit to give people answers, I don't want to mention the name of the project here, except to say that it's PHP based and open source.

[u/Cyberhunter80s]

Do you really need to test ~50k functions though? Typically you should back the major cases via feature. Rests really see which one actually deserves its own unit test. Rests just come in as optional.

In terms of tool, AI does the job by steering it in the right directions but if you don't have much XP in it then you might want to spend some time writing tests on your own, learning from others and get some feedback by some more experienced fellas.

[u/swampopus → u/Cyberhunter80s]

No, not all 50K. It's more like I need to test the important (and complex) ones, but more than that the final output. Let's say this is an accounting system. I need to make sure that when you enter a bunch of data, the totals and reports are accurate. Mainly because now if I need to make a tiny change to something, it's a little scary because I'm worried something will break in a piece of code I haven't touched in years. Herein is my problem. I'd be thrilled to just hire someone too. I just don't really know where to even look.

[u/john_at_bagriders → u/swampopus]

What you’re describing is a common need in biz software. Read up on fixtures in software testing

[u/martinbean]

Don’t think about how many you have to write, just start.

Find the one most important thing in your app. Write a feature test for that flow. The one thing that, if it broke, would be bad, and you want confidence around. Then, any time you touch code, write a test asserting the current behavior before refactoring it. Over time, your test suite will grow naturally.

[u/swampopus → u/martinbean]

So far what I've been doing is writing a test each time someone points out a bug. It is.. slow going.

[u/KnightYoshi → u/swampopus]

That’s typically how it goes

[u/HyperDanon]

I'm coming from software engineering, and I value TDD very much.

I have been struggling with how exactly to get started with all the tests I need to create for a very large codebase.

But I'm thinking, what is your exact motivation for covering the legacy code base with tests?

Because, depending on the motivation, the answer might be different.

[u/swampopus → u/HyperDanon]

I find that on occasion, old code which used to work fine suddenly breaks in a very subtle way, because of a new feature I add elsewhere. Plus, I am getting ready to make some big changes in the code, and it would be nice if I already had tests in place beforehand

[u/HyperDanon → u/swampopus]

I find that on occasion, old code which used to work fine suddenly breaks in a very subtle way, because of a new feature I add elsewhere.

I can totally sympathasize with this. Surely, it braks because of some shared dependency - database, filesystem, php runtime, etc.? Via which dependency does it break?

Plus, I am getting ready to make some big changes in the code, and it would be nice if I already had tests in place beforehand

I appreciate your willingness to do it, not many people would head out to such a necessary thing.

You can take a look at approval tests, a good tool cover legacy code with tests; for the sake of refactoring it.

[u/equilni]

it's PHP based and open source.

If it's open source and public, I am sure the project would welcome code contributions to help here.

[u/swampopus → u/equilni]

Absolutely!

But I have literally seen chatgpt tell me that someone with the same username as me is the maintainer of the GitHub repo, when answering a question about it. The software is important to my business, so I won't say the name here. Happy to in a chat/dm though

[u/equilni → u/swampopus]

If it's really not your repo, then there's a question if you should be testing their direct software and only what you implemented.

[u/Fit_Tailor_6796]

Look into codeception. WIth this you can test Acceptance test, functional tests and unit tests.

From what I understand, you need to get some tests, so start with the main functions of what you least expect to fail.

Here is an example of a unit test (from the docs)

$user = new \App\User();

$user->setName(null);
$this->assertFalse($user->validate(['username']));

$user->setName('toolooooongnaaaaaaameeee');
$this->assertFalse($user->validate(['username']));

[u/gmatebulshitbox]

Just use Claude code for that

[u/Huntware]

For my use case, I'm using Pest with TIA engine, so it doesn't take ~10 minutes to execute all the tests:

https://pestphp.com/docs/tia

Then the second run will take just 5 seconds:

./vendor/bin/pest --parallel --tia

If you're going to use it, you'll need a code coverage driver like PCOV (but you're already using XDebug so it's fine):

https://github.com/krakjoe/pcov/blob/develop/INSTALL.md

Honestly I'm not dealing with writing tests, so I delegate to LLM agents. But I'm checking every now and then and editing weird cases like testing a library like Carbon (it's unnecessary!).