Software Architect's Handbook

Where to start writing tests?

It can be difficult to know where to start when introducing unit testing in a legacy application. One approach is to start with the logic that is related to the most critical business functionality. With this approach, you will have unit test coverage for the most important components first.

Another approach is to consider the level of complexity of the components. Some people prefer to get the most complicated work out of the way first. An experienced development team may prefer this approach. Others would prefer to begin with less complex components and build up to the ones that will require more work. This approach may be more suited to a less experienced team.

When using the complexity level as a factor when ...