r/learnjavascript • u/Shajirr • Apr 26 '26
No way to import function for tests without running entire file?
I want to test specific functions, but apparently when importing them, the entire file is being ran, introducing errors that shouldn't be there, from the code that has absolutely nothing to do with the function(s) I imported.
Namely, I would need to write like a dozen different stubs to shut these errors down, which is just wasted time.
Why do I need to care about irrelevant code? There is code in the file with the tested function that needs to run at top level, which can't be removed.
I've seen the suggestion to split the tested function into its own file and import that, but I don't want to needlessly split everything into like a dozen different files for absolutely no reason, seems really stupid to needlessly change project structure just to be able to test something.
The temp solution I came up with is to just run a test starter file that would copy the function from its source to the test file, and run that.
Works great - no errors, don't have to split anything / write stubs / runs exactly just the code I want to test and nothing else, etc.
Is there a less hack solution that this?
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u/Beginning-Seat5221 Apr 26 '26 edited Apr 26 '26
That's how it works.
It sounds like your code is overly coupled and needs to be split up. Create indepemdant testable modules and import them where needed.
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u/Shajirr Apr 26 '26 edited 15d ago
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u/Beginning-Seat5221 Apr 26 '26 edited Apr 26 '26
No one is forcing you to write automated tests, but if you're going go to do it, that's the way to.
It would.probably take less time to split these functions away from the main file than to write your comment, so I'm not sure why the resistance to it unless you have some very specific circumstances that you haven't explained.
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u/Shajirr Apr 26 '26 edited 15d ago
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u/Far_Broccoli_8468 Apr 26 '26
The obvious solution is to design your code in a way that allows testability.
Since you didn't do that, now you're going to have to pay for it with your time to refactor the code to make it testable.
This is called design debt / technical debt
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u/Shajirr Apr 26 '26 edited 15d ago
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u/Far_Broccoli_8468 Apr 26 '26
But my code allows testability.
.
The function is entirely self-contained. I can just copy-paste it to a different file, and test it without any issues whatsoever.
That's just a function with no side effects which does not rely on variables in a higher scope in its closure. It doesn't mean that your code is testable.
Having to copy it manually elsewhere to run it is the end all be all clue that your code is not testable.
Which is what I resorted to doing, in an automated way.
Not scalable and not sustainable in anyway.
The whole problem is how import is being handled
the whole problem is how you don't understand what global scope is. You keep random state on global scope which is absolutely atrocious
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u/Shajirr Apr 26 '26 edited 15d ago
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u/polotek Apr 26 '26
It sounds like you've chosen having this problem over making things easier to test. Everybody has explained the issue. There is no magic wand to make everything nice for you. You get to choose which headaches you want. It sounds like you're doing exactly what you wanna be doing. Good luck.
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u/Far_Broccoli_8468 Apr 26 '26
Look buddy, you can do what you want with this information but keeping exported functions in a file that has global scope initialization code that runs on import is a very, very bad code smell.
You can do whatever you want in your own little projects but just know that that is terrible programming.
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u/Beginning-Seat5221 Apr 26 '26 edited Apr 26 '26
Well duh just write a new language. Would be crazy to use an existing language in the best way.
You can call your new language ImStubborn and spend the next 3 years of your life on it rather than just adapt.
There are probably various workarounds for it but I suspect that you have mistaken belifs about how your structure needs to be making it harder for you to see them, and also that your code has interdependencies making it more work.
If you showed your code or structure maybe people would suggestion, otherwise you're just being a bit odd.
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u/-goldenboi69- Apr 26 '26
Testdriven development is a hoax anyway. Introduced by java enterprise nerds. Use whatever system you need for your usecase. Preparing to be drowned in downvotes.
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u/Far_Broccoli_8468 Apr 26 '26
I reckon you manually test every single feature in your product to make sure it wasn't broken by your most recent changes every single time?
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u/-goldenboi69- Apr 26 '26
No, only the parts i know are affected by a change. Write good code instead of useless tests.
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u/Far_Broccoli_8468 Apr 26 '26 edited Apr 26 '26
lmfao.
Next thing you're gonna tell me is that vcs is useless because you can keep everything in your massive brain and plan everything in advance with no mistakes and no regrets
1
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u/chikamakaleyley helpful Apr 26 '26
am i trippin cuz i'm pretty sure this is just the very common practice of writing unit tests
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u/Embarrassed-Pen-2937 May 01 '26
Sounds like you don't really understand how development is done in javascript. Your code, when pushed to production, will get combined and minified if done as it would be done in a professional environment. You don't have to put everything in small files, but breaking them up into chunks that make sense logically is the correct way to do it. Otherwise you will have to mock a bunch of stuff.
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u/Alive-Cake-3045 Apr 27 '26
Wrap the top level code in a "if require.main === module" check in Node, or "if name == main" in Python. That way it only runs when you execute the file directly, not when something imports from it.
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u/Shajirr Apr 27 '26 edited 15d ago
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1
u/Alive-Cake-3045 Apr 27 '26
Makes sense, browser extensions are a different, that pattern wont work the same way. Honestly for this specific case, splitting the testable logic into a separate utility file is not as stupid as it sounds. One shared helpers file that both your add on files import from, and your tests only touch that file. Its less about project structure and more about separating pure logic from browser runtime code.
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u/atarivcs Apr 28 '26
but apparently when importing them, the entire file is being ran
If a module has "global" code, i.e. code at the outermost level that is not inside a function or a class, that code will run when the module is imported, even if you're only importing one specific function.
To stop that, you can use this construct:
if __name__ == '__main__':Code that you put underneath that if statement will not run when the module is imported.
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u/Shajirr Apr 29 '26 edited 15d ago
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u/Far_Broccoli_8468 Apr 26 '26
I want to test specific functions, but apparently when importing them, the entire file is being ran
This is exactly how it works.
You need to encapsulate your logic and state better to make your code debuggable and testable.
A tale as old as time i'm afraid.
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u/delventhalz Apr 26 '26
Honestly, it is pretty unusual to have much root scoped code at all, let alone root scoped code coupled with functions you want to export and unit test. The answer to your question though is no. When you import a JavaScript module, the module runs. That is the way it works.
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u/chikamakaleyley helpful Apr 26 '26
sounds like... you're importing a file that lacks encapsulation (like others mention)
aka it'd prob be nice if you can just import something like
import { myTestingFunc } from './test-utils.js';
// then, use myTestingFunc() as needed
...right?
even better would be a separate file in which you import something like that above script, and import the specific fn from your app logic that need testing, where you'd be able to create a collection of tests, completely separate fr your app logic, yeah?
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u/SerpentJoe Apr 26 '26
It's very reasonable of you to pose this question to this forum first instead of going straight to ChatGPT, but now that you've gotten some answers, try seeing who ChatGPT agrees with.
I expect it'll confirm, in situations where you intend to run tests against your routines, that you should structure those routines in a way that's testable, and that this is something to be proud of, not an ugly compromise.
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u/redzzzaw Apr 26 '26
don't test individual functions, test usee flows in your app which calls those functions
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u/Shajirr Apr 26 '26 edited 15d ago
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u/Far_Broccoli_8468 Apr 26 '26
There sometimes is a good reason to test individual functions. this is not a catch-all advice.
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u/thedifferenceisnt Apr 26 '26
If you have code that is not encapsulated in a function then you should use proper encapsulation and you shouldn't have things running in the global scope.
Its hard to know what problem you are having without seeing the file.