When you need to write or modify some T-SQL code, you may be tempted to just start writing the code. In many cases, the necessary database code is simple enough that no additional analysis is needed. Eventually, there always comes a scenario where the data being queried or the T-SQL code is complex enough where you want to make certain that your code is working as expected. During these times, you might find that you want to test your T-SQL changes. While you can start testing T-SQL code at any time, you may find it helpful to start the habits early on before dealing with complex scenarios.