C#•3y ago

Unit Testing Classes with Dependency Injection (ASP.NET Core)

How do you guys usually handle this? I saw some people mock every single injection which seems pretty horrible, other people end up in a way where they effectively have to rebuild the Program.cs class in their test project.

I'm using xUnit

To be a little more clear. The class I want to test on takes in some interfaces via dependency injection in it's constructor, and these are used in the methods I want to test. - Ideally, I want them to function how they actually would, using the concerete classes injected

Pobiega•9/15/23, 1:14 PM

If you want to use the real implementations, then do that.

PibblesOP•9/15/23, 1:15 PM

Do what? Rebuild Prpgram.cs?

Pobiega•9/15/23, 1:15 PM

no, use teh real implementations

Pobiega•9/15/23, 1:15 PM

you could assemble a serviceprovider based on the real one from program if you want, or you just do var sut = new Sut(new dep1, new dep2)var sut = new Sut(new dep1, new dep2) etc if thats feasible

Pobiega•9/15/23, 1:16 PM

it all depends on your setup and how complicated your dependency graph is

Pobiega•9/15/23, 1:17 PM

the reason mocking all dependencies is common is because

its easy
it makes your tests true unit tests (testing a distinct "unit" of code)

PibblesOP•9/15/23, 1:18 PM

Well those interfaces, the real implementation might also take some interfaces. And if I swap the concrete class I’m using for something I don’t want to have to go through every unit test and change it manually.
As far as mocking each interface, I’d be okay with it, but then if I change the way that method works I’m again having to go to each unit test and change it

PibblesOP•9/15/23, 1:19 PM

And one of the interfaces is a mapper, so any change to the object I’m mapping and I’ll have to change them all etc

Pobiega•9/15/23, 1:19 PM

Well those interfaces, the real implementation might also take some interfaces

Sure, so use dependency injection to resolve your service under test?

PibblesOP•9/15/23, 1:19 PM

Yeah I was just checking there wasn’t some simpler way people used but it seems like this is still the best

Pobiega•9/15/23, 1:21 PM

honestly if you want to test like this (which is perfectly fine btw), I'd consider using WebApplicationFactory and TestingContainers (for a database or similar) and making full on integration tests

Pobiega•9/15/23, 1:21 PM

why stop half the way there

PPobiega why stop half the way there 🙂

PibblesOP•9/15/23, 1:24 PM

I mean, these should just be unit tests

Pobiega•9/15/23, 1:25 PM

they are not

Pobiega•9/15/23, 1:25 PM

if you are testing a service that has real dependencies that do actual work, thats no longer a unit by most definitions

Pobiega•9/15/23, 1:25 PM

"Half my codebase is one unit" is a weird border

Pobiega•9/15/23, 1:26 PM

if a single test "tests" a huge portion of your app, thats really close to a full E2E or integration test already

PibblesOP•9/15/23, 1:27 PM

I mean I would mock them if it weren't such a pain to do so
but I'd say that if it's still internal to the project, and not using the more external stuff like a database, I'd still think of it as a unit test

Pobiega•9/15/23, 1:27 PM

these are just terms for distinction btw, you can still use xUnit to make e2e or integration tests

PibblesOP•9/15/23, 1:27 PM

it's not using a huge portion at all

PibblesOP•9/15/23, 1:27 PM

it's basically using a helper method

PibblesOP•9/15/23, 1:27 PM

it's using a mapper

Pobiega•9/15/23, 1:27 PM

right

PibblesOP•9/15/23, 1:28 PM

it's just that mocking the mapper is probably going to cause more pain down the line if I change the mapper or the object coming out

PibblesOP•9/15/23, 1:28 PM

PibblesOP•9/15/23, 1:29 PM

maybe I should just mock it anyway

Pobiega•9/15/23, 1:29 PM

mocking a mapper does indeed sound painful

Pobiega•9/15/23, 1:29 PM

Then again

PibblesOP•9/15/23, 1:29 PM

it would make it more of a unit test you are right there, since rn it would effectively be testing the mapper

Pobiega•9/15/23, 1:29 PM

I very rarely if ever use mappers in a service

Pobiega•9/15/23, 1:29 PM

I prefer to do that at the endpoint level

Pobiega•9/15/23, 1:29 PM

the service/command/etc is part of the domain, so it operates on domain objects

Pobiega•9/15/23, 1:30 PM

your opinion might vary, and thats fine too

PibblesOP•9/15/23, 1:30 PM

oh I'm probably just naming stuff wrong tbh

Pobiega•9/15/23, 1:30 PM

I don't think you are

Pobiega•9/15/23, 1:30 PM

but perhaps

PibblesOP•9/15/23, 1:31 PM

I have the API, which is made up of the controller method -> service layer (handles business logic and calls mapper service) -> data access layer (contains no business logic)

Pobiega•9/15/23, 1:31 PM

thats exactly what I assumed yes

Pobiega•9/15/23, 1:31 PM

I don't do mapping in the service layer

Pobiega•9/15/23, 1:31 PM

its not a service concern, imho

Pobiega•9/15/23, 1:31 PM

its an API concern

Pobiega•9/15/23, 1:32 PM

I could see a world where you reuse your domain/data/service layers for lets say a console app, and you want a different shape on the resulting data

PibblesOP•9/15/23, 1:32 PM

would you not test your controller method though?

Pobiega•9/15/23, 1:32 PM

not via a unit test

Pobiega•9/15/23, 1:32 PM

integration test, maybe

Pobiega•9/15/23, 1:33 PM

but since my controllers are literally just "model bind a http request, issue a command based on that data, map result, return result"

Pobiega•9/15/23, 1:33 PM

its not really a huge consideration

Pobiega•9/15/23, 1:33 PM

every single command (or service, in your case) is ofc tested

PibblesOP•9/15/23, 1:33 PM

yeah mine is that without the mapping lmao

Pobiega•9/15/23, 1:33 PM

and I usually have tests for my mappers too, if they are not trivial

Unit Testing Classes with Dependency Injection (ASP.NET Core)

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