Dummy data and unit testing strategies in a modular application stack

Question

How do you manage dummy data used for tests? Keep them with their respective entities? In a separate test project? Load them with a Serializer from external resources? Or just r

Answer 1

Well, I read carefully all evaluations so far, and it is very good question. I see following approaches to the problem:

1. Set up (static) test data base;
2. Each test has it's own set up data that creates (dynamic) test data prior to running unit tests;
3. Use dummy or mock object. All modules know all dummy objects, this way there is no duplicates;
4. Reduce the scope of the unit test;

First option is pretty straight forward and has many drawbacks, somebody has to reproduce it's once in while, when unit tests "mess it up", if there are changes in the data-module, somebody has to introduce corresponding changes to the test data, a lot of maintenance overhead. Not to say that generation of this data on the first hand maybe tricky. See aslo second option.

Second option, you write your test code that prior to the testing invokes some of your "core" business methods that creates your entity. Ideally, your test code should be independent from the production code, but in this case, you will end up with duplicate code, that you should support twice. Sometimes, it is good to split your production business method in order to have entry point for your unit test (I makes such methods private and use Reflection to invoke them, also some remark on the method is needed, refactoring is now a bit tricky). The main drawback that if you must change your "core" business methods it suddenly effects all of your unit test and you can't test. So, developers should be aware of it and not make partials commits to the "core" business methods, unless they works. Also, with any change in this area, you should keep in your mind "how it will affect my unit test". Sometimes also, it is impossible to reproduce all the required data dynamically (usually, it is because of the third-parties API, for example, you call another application with it's own DB from which you required to use some keys. This keys (with the associated data) is created manually through third-party application. In such a case, this data and only this data, should be created statically. For example, your created 10000 keys starting from 300000.

Third option should be good. Options a) and d) sounds for me pretty good. For your dummy object you can use the mock framework or you can not to use it. Mock Framework is here only to help you. I don't see problem that all of your unit know all your entities.

Fourth option means that you redefine what is "unit" in your unit test. When you have couple of modules with interdependence than it can be difficult to test each module in isolation. This approach says, that what we originally tested was integration test and not unit test. So, we split our methods, extract small "units of works" that receives all it's interdependences to another modules as parameters. This parameters can be (hopefully) easily mocked up. The main drawback of this approach, that you don't test all of your code, but only so to say, the "focal points". You need to make integration test separately (usually by QA team).