CODEWITHSUNDEEP
unit-testingtestingdependencies
user802232
user802232

Reputation: 2611

On dependencies in unit testing

I am new to unit testing, but tend to think that I believe in beautifully written code, and properly designed architectures.

My question is. Aren't unit tests focusing too much on dependencies between objects? What do you do when your unit test fails because a dependency your method used to call befor is no longer called (a design decision) or your method calls another method or a dependency (again a design decision) Do you redesign your tests? If that's the case, then unit testing helps very little to reduce couple and improve cohesion between components.

Maybe my opinion is too broad, but in general how do people treat dependencies in properly mannered unit tests. I guess that the best way would be to have no dependencies at all, and every method relied on the parameters that were given to it, but this is hardly the case in reality. In addition, faking every dependency method for every possible call is also a bit subjective and time wasting, because at a future point in time, the class under test may simply no longer need the dependency.

Upvotes: 1

Views: 2712

Answers (3)

philant
philant

Reputation: 35806

Unit tests shall test the behavior, not the implementation. That way, one can rely on the unit tests when changing the implementation, or when refactoring the code. Removing a dependency (via inlining the class for instance), does not break the test.

Testing the implementation leads to brittle tests, that gets in the way when refactoring.

Upvotes: 1

Jason Evans
Jason Evans

Reputation: 29186

I would suggest that you look at Test Driven Development (TDD) as I believe this technique will help you with your design issues. By writing unit tests before writing the production code, you will need to think about how to make your production code testable. This is better then the test later approach, where you write the production code first and then try to shoe-horn tests around them.

To deal with dependencies, think about what dependencies are causing you problems.

External Dependencies

If your tests use an external resource, such as a file, then you are writing an integration test, not a unit test. I've written many tests that use an external file, and I simply created a copy of the file in my test project. This file copy will contain dummy data required for my tests.

If your test requires a database, then again your writing an integration test. Personally I create a local copy of the database on my PC and run my tests against it.

Object Dependencies

If you are worried about code dependencies (e.g. your test will fail if a private method's signature is changed) then you are testing at the wrong level of abstraction. By that I mean make sure that your tests are calling public API's and not private ones. To cement this point, use interfaces for your objects to ensure an expected contract for an object that implements it.

I would also recommend that you try using a mocking framework such as RhinoMocks, Moq or TypeMock

A mocking framework will help you remove the dependency on, for example, having a database available for your tests. I personally use TypeMock, it's not cheap but it's by far the most powerful tool out there.

Upvotes: 2

khmarbaise
khmarbaise

Reputation: 97359

If you are talking about Unit testing you have no dependencies, cause a unit test tests only a single class (Java, C++, Ruby, Python). What you are talking about sounds more like integration testing which is different. Furthermore if you have to much dependencies your coupling is to high which is not very good, but of course not always avoidable.

Upvotes: 0

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