The product I have been working on has been in development for the past six years. It started as a generic data entry portal into an insanely complex part WPF/part legacy application. The system has been developed for all these years without a single Unit test in its fold. Now, the point has been raised for a comprehensive unit testing framework. I have been recruited recently to work on this product and have been tasked to get the ‘Testing’ in order. Since the team that worked on the product for the last six years adopted ‘Agile’, the project lacks any documentation of the business rules or any design documents.
I have been trying to write unit tests for some of the modules. But I am not sure what to Mock, how to setup my Test fixture and eventually what to Test for, since a casual glance of the methods does not reveal its intentions. Also, it has come to my attention that the code was not developed with a particular methodology in mind.
Given the situation, I was wondering if the good people of Stackoverflow could provide me with some advise on how to salvage this situation. I have heard about the book ‘Working with Legacy Code’ that has something to say about this general situation but I was thinking about getting some pointers from individuals who have encountered similar situations within the technology stack(C#,VB,C++,.NET 3.5,WCF,SQL Server 2005).
In my opinion the best way is to start by “stabilizing” the current code functionallity using integration tests. Try to create tests that has start point which is not likely to change later. Using the integration tests you can gain confidence that refactoring that’ll come later for the unit tests are not breaking anything.
The next step is to unit test the code. If you’re free to refactor the code you can start separating logic to classes (e.g. extra logic in view layer) and add unit tests to them. Using this process you also get to know better the code of the product.
It is very recommended read Working with Legacy Code, many of the problems you’re going to encounter already have solutions 🙂
Unit testing legacy code can be a challenge sometimes, depending on the existing code and on how much you can change the code. You can use some tools, for example for writing integration tests you can use White framework to automate the GUI. Another tool you can use for writing the unit tests without forcing major changes in the code is Typemock Isolator (disclaimer – I work at Typemock), it allows faking most of dependencies without changing the production code. There are many other tools which can ease the process, try to find and make best use of them 🙂